X-Git-Url: https://www.ginac.de/ginac.git//ginac.git?p=ginac.git;a=blobdiff_plain;f=ginac%2Fmatrix.cpp;h=8a68b663b90293a318e445bf8f5801980490e901;hp=f76aa9d768f0de53419c0285ebf9fc9485226596;hb=f7a07ae7330a3543bb00aa7b659e2624d6c440c7;hpb=af0c47009ca7a15af966430bdf1a72fe05c1c6f9

diff --git a/ginac/matrix.cpp b/ginac/matrix.cpp
index f76aa9d7..8a68b663 100644
--- a/ginac/matrix.cpp
+++ b/ginac/matrix.cpp
@@ -3,7 +3,7 @@
  *  Implementation of symbolic matrices */
 
 /*
- *  GiNaC Copyright (C) 1999-2000 Johannes Gutenberg University Mainz, Germany
+ *  GiNaC Copyright (C) 1999-2001 Johannes Gutenberg University Mainz, Germany
  *
  *  This program is free software; you can redistribute it and/or modify
  *  it under the terms of the GNU General Public License as published by
@@ -25,74 +25,45 @@
 #include <stdexcept>
 
 #include "matrix.h"
-#include "archive.h"
 #include "numeric.h"
 #include "lst.h"
-#include "utils.h"
-#include "debugmsg.h"
+#include "idx.h"
+#include "indexed.h"
 #include "power.h"
 #include "symbol.h"
 #include "normal.h"
+#include "print.h"
+#include "archive.h"
+#include "utils.h"
+#include "debugmsg.h"
 
-#ifndef NO_NAMESPACE_GINAC
 namespace GiNaC {
-#endif // ndef NO_NAMESPACE_GINAC
 
 GINAC_IMPLEMENT_REGISTERED_CLASS(matrix, basic)
 
 //////////
-// default constructor, destructor, copy constructor, assignment operator
-// and helpers:
+// default ctor, dtor, copy ctor, assignment operator and helpers:
 //////////
 
-// public
-
 /** Default ctor.  Initializes to 1 x 1-dimensional zero-matrix. */
-matrix::matrix()
-    : inherited(TINFO_matrix), row(1), col(1)
-{
-    debugmsg("matrix default constructor",LOGLEVEL_CONSTRUCT);
-    m.push_back(_ex0());
-}
-
-matrix::~matrix()
+matrix::matrix() : inherited(TINFO_matrix), row(1), col(1)
 {
-    debugmsg("matrix destructor",LOGLEVEL_DESTRUCT);
+	debugmsg("matrix default ctor",LOGLEVEL_CONSTRUCT);
+	m.push_back(_ex0());
 }
 
-matrix::matrix(const matrix & other)
-{
-    debugmsg("matrix copy constructor",LOGLEVEL_CONSTRUCT);
-    copy(other);
-}
-
-const matrix & matrix::operator=(const matrix & other)
-{
-    debugmsg("matrix operator=",LOGLEVEL_ASSIGNMENT);
-    if (this != &other) {
-        destroy(1);
-        copy(other);
-    }
-    return *this;
-}
-
-// protected
-
 void matrix::copy(const matrix & other)
 {
-    inherited::copy(other);
-    row = other.row;
-    col = other.col;
-    m = other.m;  // STL's vector copying invoked here
+	inherited::copy(other);
+	row = other.row;
+	col = other.col;
+	m = other.m;  // STL's vector copying invoked here
 }
 
-void matrix::destroy(bool call_parent)
-{
-    if (call_parent) inherited::destroy(call_parent);
-}
+DEFAULT_DESTROY(matrix)
 
 //////////
-// other constructors
+// other ctors
 //////////
 
 // public
@@ -102,230 +73,471 @@ void matrix::destroy(bool call_parent)
  *  @param r number of rows
  *  @param c number of cols */
 matrix::matrix(unsigned r, unsigned c)
-    : inherited(TINFO_matrix), row(r), col(c)
+  : inherited(TINFO_matrix), row(r), col(c)
 {
-    debugmsg("matrix constructor from unsigned,unsigned",LOGLEVEL_CONSTRUCT);
-    m.resize(r*c, _ex0());
+	debugmsg("matrix ctor from unsigned,unsigned",LOGLEVEL_CONSTRUCT);
+	m.resize(r*c, _ex0());
 }
 
- // protected
+// protected
 
 /** Ctor from representation, for internal use only. */
 matrix::matrix(unsigned r, unsigned c, const exvector & m2)
-    : inherited(TINFO_matrix), row(r), col(c), m(m2)
+  : inherited(TINFO_matrix), row(r), col(c), m(m2)
 {
-    debugmsg("matrix constructor from unsigned,unsigned,exvector",LOGLEVEL_CONSTRUCT);
+	debugmsg("matrix ctor from unsigned,unsigned,exvector",LOGLEVEL_CONSTRUCT);
+}
+
+/** Construct matrix from (flat) list of elements. If the list has fewer
+ *  elements than the matrix, the remaining matrix elements are set to zero.
+ *  If the list has more elements than the matrix, the excessive elements are
+ *  thrown away. */
+matrix::matrix(unsigned r, unsigned c, const lst & l)
+  : inherited(TINFO_matrix), row(r), col(c)
+{
+	debugmsg("matrix ctor from unsigned,unsigned,lst",LOGLEVEL_CONSTRUCT);
+	m.resize(r*c, _ex0());
+
+	for (unsigned i=0; i<l.nops(); i++) {
+		unsigned x = i % c;
+		unsigned y = i / c;
+		if (y >= r)
+			break; // matrix smaller than list: throw away excessive elements
+		m[y*c+x] = l.op(i);
+	}
 }
 
 //////////
 // archiving
 //////////
 
-/** Construct object from archive_node. */
 matrix::matrix(const archive_node &n, const lst &sym_lst) : inherited(n, sym_lst)
 {
-    debugmsg("matrix constructor from archive_node", LOGLEVEL_CONSTRUCT);
-    if (!(n.find_unsigned("row", row)) || !(n.find_unsigned("col", col)))
-        throw (std::runtime_error("unknown matrix dimensions in archive"));
-    m.reserve(row * col);
-    for (unsigned int i=0; true; i++) {
-        ex e;
-        if (n.find_ex("m", e, sym_lst, i))
-            m.push_back(e);
-        else
-            break;
-    }
-}
-
-/** Unarchive the object. */
-ex matrix::unarchive(const archive_node &n, const lst &sym_lst)
-{
-    return (new matrix(n, sym_lst))->setflag(status_flags::dynallocated);
+	debugmsg("matrix ctor from archive_node", LOGLEVEL_CONSTRUCT);
+	if (!(n.find_unsigned("row", row)) || !(n.find_unsigned("col", col)))
+		throw (std::runtime_error("unknown matrix dimensions in archive"));
+	m.reserve(row * col);
+	for (unsigned int i=0; true; i++) {
+		ex e;
+		if (n.find_ex("m", e, sym_lst, i))
+			m.push_back(e);
+		else
+			break;
+	}
 }
 
-/** Archive the object. */
 void matrix::archive(archive_node &n) const
 {
-    inherited::archive(n);
-    n.add_unsigned("row", row);
-    n.add_unsigned("col", col);
-    exvector::const_iterator i = m.begin(), iend = m.end();
-    while (i != iend) {
-        n.add_ex("m", *i);
-        i++;
-    }
+	inherited::archive(n);
+	n.add_unsigned("row", row);
+	n.add_unsigned("col", col);
+	exvector::const_iterator i = m.begin(), iend = m.end();
+	while (i != iend) {
+		n.add_ex("m", *i);
+		++i;
+	}
 }
 
+DEFAULT_UNARCHIVE(matrix)
+
 //////////
 // functions overriding virtual functions from bases classes
 //////////
 
 // public
 
-basic * matrix::duplicate() const
-{
-    debugmsg("matrix duplicate",LOGLEVEL_DUPLICATE);
-    return new matrix(*this);
-}
-
-void matrix::print(ostream & os, unsigned upper_precedence) const
-{
-    debugmsg("matrix print",LOGLEVEL_PRINT);
-    os << "[[ ";
-    for (unsigned r=0; r<row-1; ++r) {
-        os << "[[";
-        for (unsigned c=0; c<col-1; ++c) {
-            os << m[r*col+c] << ",";
-        }
-        os << m[col*(r+1)-1] << "]], ";
-    }
-    os << "[[";
-    for (unsigned c=0; c<col-1; ++c) {
-        os << m[(row-1)*col+c] << ",";
-    }
-    os << m[row*col-1] << "]] ]]";
-}
-
-void matrix::printraw(ostream & os) const
+void matrix::print(const print_context & c, unsigned level) const
 {
-    debugmsg("matrix printraw",LOGLEVEL_PRINT);
-    os << "matrix(" << row << "," << col <<",";
-    for (unsigned r=0; r<row-1; ++r) {
-        os << "(";
-        for (unsigned c=0; c<col-1; ++c) {
-            os << m[r*col+c] << ",";
-        }
-        os << m[col*(r-1)-1] << "),";
-    }
-    os << "(";
-    for (unsigned c=0; c<col-1; ++c) {
-        os << m[(row-1)*col+c] << ",";
-    }
-    os << m[row*col-1] << "))";
+	debugmsg("matrix print", LOGLEVEL_PRINT);
+
+	if (is_of_type(c, print_tree)) {
+
+		inherited::print(c, level);
+
+	} else {
+
+		c.s << "[[ ";
+		for (unsigned y=0; y<row-1; ++y) {
+			c.s << "[[";
+			for (unsigned x=0; x<col-1; ++x) {
+				m[y*col+x].print(c);
+				c.s << ",";
+			}
+			m[col*(y+1)-1].print(c);
+			c.s << "]], ";
+		}
+		c.s << "[[";
+		for (unsigned x=0; x<col-1; ++x) {
+			m[(row-1)*col+x].print(c);
+			c.s << ",";
+		}
+		m[row*col-1].print(c);
+		c.s << "]] ]]";
+
+	}
 }
 
 /** nops is defined to be rows x columns. */
 unsigned matrix::nops() const
 {
-    return row*col;
+	return row*col;
 }
 
 /** returns matrix entry at position (i/col, i%col). */
 ex matrix::op(int i) const
 {
-    return m[i];
+	return m[i];
 }
 
 /** returns matrix entry at position (i/col, i%col). */
 ex & matrix::let_op(int i)
 {
-    return m[i];
+	GINAC_ASSERT(i>=0);
+	GINAC_ASSERT(i<nops());
+	
+	return m[i];
 }
 
 /** expands the elements of a matrix entry by entry. */
 ex matrix::expand(unsigned options) const
 {
-    exvector tmp(row*col);
-    for (unsigned i=0; i<row*col; ++i) {
-        tmp[i]=m[i].expand(options);
-    }
-    return matrix(row, col, tmp);
+	exvector tmp(row*col);
+	for (unsigned i=0; i<row*col; ++i)
+		tmp[i] = m[i].expand(options);
+	
+	return matrix(row, col, tmp);
 }
 
 /** Search ocurrences.  A matrix 'has' an expression if it is the expression
  *  itself or one of the elements 'has' it. */
 bool matrix::has(const ex & other) const
 {
-    GINAC_ASSERT(other.bp!=0);
-    
-    // tautology: it is the expression itself
-    if (is_equal(*other.bp)) return true;
-    
-    // search all the elements
-    for (exvector::const_iterator r=m.begin(); r!=m.end(); ++r) {
-        if ((*r).has(other)) return true;
-    }
-    return false;
+	GINAC_ASSERT(other.bp!=0);
+	
+	// tautology: it is the expression itself
+	if (is_equal(*other.bp)) return true;
+	
+	// search all the elements
+	for (exvector::const_iterator r=m.begin(); r!=m.end(); ++r)
+		if ((*r).has(other)) return true;
+	
+	return false;
 }
 
-/** evaluate matrix entry by entry. */
+/** Evaluate matrix entry by entry. */
 ex matrix::eval(int level) const
 {
-    debugmsg("matrix eval",LOGLEVEL_MEMBER_FUNCTION);
-    
-    // check if we have to do anything at all
-    if ((level==1)&&(flags & status_flags::evaluated))
-        return *this;
-    
-    // emergency break
-    if (level == -max_recursion_level)
-        throw (std::runtime_error("matrix::eval(): recursion limit exceeded"));
-    
-    // eval() entry by entry
-    exvector m2(row*col);
-    --level;    
-    for (unsigned r=0; r<row; ++r) {
-        for (unsigned c=0; c<col; ++c) {
-            m2[r*col+c] = m[r*col+c].eval(level);
-        }
-    }
-    
-    return (new matrix(row, col, m2))->setflag(status_flags::dynallocated |
-                                               status_flags::evaluated );
+	debugmsg("matrix eval",LOGLEVEL_MEMBER_FUNCTION);
+	
+	// check if we have to do anything at all
+	if ((level==1)&&(flags & status_flags::evaluated))
+		return *this;
+	
+	// emergency break
+	if (level == -max_recursion_level)
+		throw (std::runtime_error("matrix::eval(): recursion limit exceeded"));
+	
+	// eval() entry by entry
+	exvector m2(row*col);
+	--level;
+	for (unsigned r=0; r<row; ++r)
+		for (unsigned c=0; c<col; ++c)
+			m2[r*col+c] = m[r*col+c].eval(level);
+	
+	return (new matrix(row, col, m2))->setflag(status_flags::dynallocated |
+											   status_flags::evaluated );
 }
 
-/** evaluate matrix numerically entry by entry. */
+/** Evaluate matrix numerically entry by entry. */
 ex matrix::evalf(int level) const
 {
-    debugmsg("matrix evalf",LOGLEVEL_MEMBER_FUNCTION);
-        
-    // check if we have to do anything at all
-    if (level==1)
-        return *this;
-    
-    // emergency break
-    if (level == -max_recursion_level) {
-        throw (std::runtime_error("matrix::evalf(): recursion limit exceeded"));
-    }
-    
-    // evalf() entry by entry
-    exvector m2(row*col);
-    --level;
-    for (unsigned r=0; r<row; ++r) {
-        for (unsigned c=0; c<col; ++c) {
-            m2[r*col+c] = m[r*col+c].evalf(level);
-        }
-    }
-    return matrix(row, col, m2);
+	debugmsg("matrix evalf",LOGLEVEL_MEMBER_FUNCTION);
+		
+	// check if we have to do anything at all
+	if (level==1)
+		return *this;
+	
+	// emergency break
+	if (level == -max_recursion_level) {
+		throw (std::runtime_error("matrix::evalf(): recursion limit exceeded"));
+	}
+	
+	// evalf() entry by entry
+	exvector m2(row*col);
+	--level;
+	for (unsigned r=0; r<row; ++r)
+		for (unsigned c=0; c<col; ++c)
+			m2[r*col+c] = m[r*col+c].evalf(level);
+	
+	return matrix(row, col, m2);
+}
+
+ex matrix::subs(const lst & ls, const lst & lr) const
+{
+	exvector m2(row * col);
+	for (unsigned r=0; r<row; ++r)
+		for (unsigned c=0; c<col; ++c)
+			m2[r*col+c] = m[r*col+c].subs(ls, lr);
+
+	return matrix(row, col, m2);
 }
 
 // protected
 
 int matrix::compare_same_type(const basic & other) const
 {
-    GINAC_ASSERT(is_exactly_of_type(other, matrix));
-    const matrix & o = static_cast<matrix &>(const_cast<basic &>(other));
-    
-    // compare number of rows
-    if (row != o.rows())
-        return row < o.rows() ? -1 : 1;
-    
-    // compare number of columns
-    if (col != o.cols())
-        return col < o.cols() ? -1 : 1;
-    
-    // equal number of rows and columns, compare individual elements
-    int cmpval;
-    for (unsigned r=0; r<row; ++r) {
-        for (unsigned c=0; c<col; ++c) {
-            cmpval = ((*this)(r,c)).compare(o(r,c));
-            if (cmpval!=0) return cmpval;
-        }
-    }
-    // all elements are equal => matrices are equal;
-    return 0;
+	GINAC_ASSERT(is_exactly_of_type(other, matrix));
+	const matrix & o = static_cast<matrix &>(const_cast<basic &>(other));
+	
+	// compare number of rows
+	if (row != o.rows())
+		return row < o.rows() ? -1 : 1;
+	
+	// compare number of columns
+	if (col != o.cols())
+		return col < o.cols() ? -1 : 1;
+	
+	// equal number of rows and columns, compare individual elements
+	int cmpval;
+	for (unsigned r=0; r<row; ++r) {
+		for (unsigned c=0; c<col; ++c) {
+			cmpval = ((*this)(r,c)).compare(o(r,c));
+			if (cmpval!=0) return cmpval;
+		}
+	}
+	// all elements are equal => matrices are equal;
+	return 0;
+}
+
+/** Automatic symbolic evaluation of an indexed matrix. */
+ex matrix::eval_indexed(const basic & i) const
+{
+	GINAC_ASSERT(is_of_type(i, indexed));
+	GINAC_ASSERT(is_ex_of_type(i.op(0), matrix));
+
+	bool all_indices_unsigned = static_cast<const indexed &>(i).all_index_values_are(info_flags::nonnegint);
+
+	// Check indices
+	if (i.nops() == 2) {
+
+		// One index, must be one-dimensional vector
+		if (row != 1 && col != 1)
+			throw (std::runtime_error("matrix::eval_indexed(): vector must have exactly 1 index"));
+
+		const idx & i1 = ex_to_idx(i.op(1));
+
+		if (col == 1) {
+
+			// Column vector
+			if (!i1.get_dim().is_equal(row))
+				throw (std::runtime_error("matrix::eval_indexed(): dimension of index must match number of vector elements"));
+
+			// Index numeric -> return vector element
+			if (all_indices_unsigned) {
+				unsigned n1 = ex_to_numeric(i1.get_value()).to_int();
+				if (n1 >= row)
+					throw (std::runtime_error("matrix::eval_indexed(): value of index exceeds number of vector elements"));
+				return (*this)(n1, 0);
+			}
+
+		} else {
+
+			// Row vector
+			if (!i1.get_dim().is_equal(col))
+				throw (std::runtime_error("matrix::eval_indexed(): dimension of index must match number of vector elements"));
+
+			// Index numeric -> return vector element
+			if (all_indices_unsigned) {
+				unsigned n1 = ex_to_numeric(i1.get_value()).to_int();
+				if (n1 >= col)
+					throw (std::runtime_error("matrix::eval_indexed(): value of index exceeds number of vector elements"));
+				return (*this)(0, n1);
+			}
+		}
+
+	} else if (i.nops() == 3) {
+
+		// Two indices
+		const idx & i1 = ex_to_idx(i.op(1));
+		const idx & i2 = ex_to_idx(i.op(2));
+
+		if (!i1.get_dim().is_equal(row))
+			throw (std::runtime_error("matrix::eval_indexed(): dimension of first index must match number of rows"));
+		if (!i2.get_dim().is_equal(col))
+			throw (std::runtime_error("matrix::eval_indexed(): dimension of second index must match number of columns"));
+
+		// Pair of dummy indices -> compute trace
+		if (is_dummy_pair(i1, i2))
+			return trace();
+
+		// Both indices numeric -> return matrix element
+		if (all_indices_unsigned) {
+			unsigned n1 = ex_to_numeric(i1.get_value()).to_int(), n2 = ex_to_numeric(i2.get_value()).to_int();
+			if (n1 >= row)
+				throw (std::runtime_error("matrix::eval_indexed(): value of first index exceeds number of rows"));
+			if (n2 >= col)
+				throw (std::runtime_error("matrix::eval_indexed(): value of second index exceeds number of columns"));
+			return (*this)(n1, n2);
+		}
+
+	} else
+		throw (std::runtime_error("matrix::eval_indexed(): matrix must have exactly 2 indices"));
+
+	return i.hold();
+}
+
+/** Sum of two indexed matrices. */
+ex matrix::add_indexed(const ex & self, const ex & other) const
+{
+	GINAC_ASSERT(is_ex_of_type(self, indexed));
+	GINAC_ASSERT(is_ex_of_type(self.op(0), matrix));
+	GINAC_ASSERT(is_ex_of_type(other, indexed));
+	GINAC_ASSERT(self.nops() == 2 || self.nops() == 3);
+
+	// Only add two matrices
+	if (is_ex_of_type(other.op(0), matrix)) {
+		GINAC_ASSERT(other.nops() == 2 || other.nops() == 3);
+
+		const matrix &self_matrix = ex_to_matrix(self.op(0));
+		const matrix &other_matrix = ex_to_matrix(other.op(0));
+
+		if (self.nops() == 2 && other.nops() == 2) { // vector + vector
+
+			if (self_matrix.row == other_matrix.row)
+				return indexed(self_matrix.add(other_matrix), self.op(1));
+			else if (self_matrix.row == other_matrix.col)
+				return indexed(self_matrix.add(other_matrix.transpose()), self.op(1));
+
+		} else if (self.nops() == 3 && other.nops() == 3) { // matrix + matrix
+
+			if (self.op(1).is_equal(other.op(1)) && self.op(2).is_equal(other.op(2)))
+				return indexed(self_matrix.add(other_matrix), self.op(1), self.op(2));
+			else if (self.op(1).is_equal(other.op(2)) && self.op(2).is_equal(other.op(1)))
+				return indexed(self_matrix.add(other_matrix.transpose()), self.op(1), self.op(2));
+
+		}
+	}
+
+	// Don't know what to do, return unevaluated sum
+	return self + other;
+}
+
+/** Product of an indexed matrix with a number. */
+ex matrix::scalar_mul_indexed(const ex & self, const numeric & other) const
+{
+	GINAC_ASSERT(is_ex_of_type(self, indexed));
+	GINAC_ASSERT(is_ex_of_type(self.op(0), matrix));
+	GINAC_ASSERT(self.nops() == 2 || self.nops() == 3);
+
+	const matrix &self_matrix = ex_to_matrix(self.op(0));
+
+	if (self.nops() == 2)
+		return indexed(self_matrix.mul(other), self.op(1));
+	else // self.nops() == 3
+		return indexed(self_matrix.mul(other), self.op(1), self.op(2));
+}
+
+/** Contraction of an indexed matrix with something else. */
+bool matrix::contract_with(exvector::iterator self, exvector::iterator other, exvector & v) const
+{
+	GINAC_ASSERT(is_ex_of_type(*self, indexed));
+	GINAC_ASSERT(is_ex_of_type(*other, indexed));
+	GINAC_ASSERT(self->nops() == 2 || self->nops() == 3);
+	GINAC_ASSERT(is_ex_of_type(self->op(0), matrix));
+
+	// Only contract with other matrices
+	if (!is_ex_of_type(other->op(0), matrix))
+		return false;
+
+	GINAC_ASSERT(other->nops() == 2 || other->nops() == 3);
+
+	const matrix &self_matrix = ex_to_matrix(self->op(0));
+	const matrix &other_matrix = ex_to_matrix(other->op(0));
+
+	if (self->nops() == 2) {
+		unsigned self_dim = (self_matrix.col == 1) ? self_matrix.row : self_matrix.col;
+
+		if (other->nops() == 2) { // vector * vector (scalar product)
+			unsigned other_dim = (other_matrix.col == 1) ? other_matrix.row : other_matrix.col;
+
+			if (self_matrix.col == 1) {
+				if (other_matrix.col == 1) {
+					// Column vector * column vector, transpose first vector
+					*self = self_matrix.transpose().mul(other_matrix)(0, 0);
+				} else {
+					// Column vector * row vector, swap factors
+					*self = other_matrix.mul(self_matrix)(0, 0);
+				}
+			} else {
+				if (other_matrix.col == 1) {
+					// Row vector * column vector, perfect
+					*self = self_matrix.mul(other_matrix)(0, 0);
+				} else {
+					// Row vector * row vector, transpose second vector
+					*self = self_matrix.mul(other_matrix.transpose())(0, 0);
+				}
+			}
+			*other = _ex1();
+			return true;
+
+		} else { // vector * matrix
+
+			// B_i * A_ij = (B*A)_j (B is row vector)
+			if (is_dummy_pair(self->op(1), other->op(1))) {
+				if (self_matrix.row == 1)
+					*self = indexed(self_matrix.mul(other_matrix), other->op(2));
+				else
+					*self = indexed(self_matrix.transpose().mul(other_matrix), other->op(2));
+				*other = _ex1();
+				return true;
+			}
+
+			// B_j * A_ij = (A*B)_i (B is column vector)
+			if (is_dummy_pair(self->op(1), other->op(2))) {
+				if (self_matrix.col == 1)
+					*self = indexed(other_matrix.mul(self_matrix), other->op(1));
+				else
+					*self = indexed(other_matrix.mul(self_matrix.transpose()), other->op(1));
+				*other = _ex1();
+				return true;
+			}
+		}
+
+	} else if (other->nops() == 3) { // matrix * matrix
+
+		// A_ij * B_jk = (A*B)_ik
+		if (is_dummy_pair(self->op(2), other->op(1))) {
+			*self = indexed(self_matrix.mul(other_matrix), self->op(1), other->op(2));
+			*other = _ex1();
+			return true;
+		}
+
+		// A_ij * B_kj = (A*Btrans)_ik
+		if (is_dummy_pair(self->op(2), other->op(2))) {
+			*self = indexed(self_matrix.mul(other_matrix.transpose()), self->op(1), other->op(1));
+			*other = _ex1();
+			return true;
+		}
+
+		// A_ji * B_jk = (Atrans*B)_ik
+		if (is_dummy_pair(self->op(1), other->op(1))) {
+			*self = indexed(self_matrix.transpose().mul(other_matrix), self->op(2), other->op(2));
+			*other = _ex1();
+			return true;
+		}
+
+		// A_ji * B_kj = (B*A)_ki
+		if (is_dummy_pair(self->op(1), other->op(2))) {
+			*self = indexed(other_matrix.mul(self_matrix), other->op(1), self->op(2));
+			*other = _ex1();
+			return true;
+		}
+	}
+
+	return false;
 }
 
+
 //////////
 // non-virtual functions in this class
 //////////
@@ -337,18 +549,16 @@ int matrix::compare_same_type(const basic & other) const
  *  @exception logic_error (incompatible matrices) */
 matrix matrix::add(const matrix & other) const
 {
-    if (col != other.col || row != other.row)
-        throw (std::logic_error("matrix::add(): incompatible matrices"));
-    
-    exvector sum(this->m);
-    exvector::iterator i;
-    exvector::const_iterator ci;
-    for (i=sum.begin(), ci=other.m.begin();
-         i!=sum.end();
-         ++i, ++ci) {
-        (*i) += (*ci);
-    }
-    return matrix(row,col,sum);
+	if (col != other.col || row != other.row)
+		throw (std::logic_error("matrix::add(): incompatible matrices"));
+	
+	exvector sum(this->m);
+	exvector::iterator i;
+	exvector::const_iterator ci;
+	for (i=sum.begin(), ci=other.m.begin(); i!=sum.end(); ++i, ++ci)
+		(*i) += (*ci);
+	
+	return matrix(row,col,sum);
 }
 
 
@@ -357,18 +567,16 @@ matrix matrix::add(const matrix & other) const
  *  @exception logic_error (incompatible matrices) */
 matrix matrix::sub(const matrix & other) const
 {
-    if (col != other.col || row != other.row)
-        throw (std::logic_error("matrix::sub(): incompatible matrices"));
-    
-    exvector dif(this->m);
-    exvector::iterator i;
-    exvector::const_iterator ci;
-    for (i=dif.begin(), ci=other.m.begin();
-         i!=dif.end();
-         ++i, ++ci) {
-        (*i) -= (*ci);
-    }
-    return matrix(row,col,dif);
+	if (col != other.col || row != other.row)
+		throw (std::logic_error("matrix::sub(): incompatible matrices"));
+	
+	exvector dif(this->m);
+	exvector::iterator i;
+	exvector::const_iterator ci;
+	for (i=dif.begin(), ci=other.m.begin(); i!=dif.end(); ++i, ++ci)
+		(*i) -= (*ci);
+	
+	return matrix(row,col,dif);
 }
 
 
@@ -377,34 +585,47 @@ matrix matrix::sub(const matrix & other) const
  *  @exception logic_error (incompatible matrices) */
 matrix matrix::mul(const matrix & other) const
 {
-    if (col != other.row)
-        throw (std::logic_error("matrix::mul(): incompatible matrices"));
-    
-    exvector prod(row*other.col);
-    
-    for (unsigned r1=0; r1<row; ++r1) {
-        for (unsigned c=0; c<col; ++c) {
-            if (m[r1*col+c].is_zero())
-                continue;
-            for (unsigned r2=0; r2<other.col; ++r2)
-                prod[r1*other.col+r2] += m[r1*col+c] * other.m[c*other.col+r2];
-        }
-    }
-    return matrix(row, other.col, prod);
+	if (this->cols() != other.rows())
+		throw (std::logic_error("matrix::mul(): incompatible matrices"));
+	
+	exvector prod(this->rows()*other.cols());
+	
+	for (unsigned r1=0; r1<this->rows(); ++r1) {
+		for (unsigned c=0; c<this->cols(); ++c) {
+			if (m[r1*col+c].is_zero())
+				continue;
+			for (unsigned r2=0; r2<other.cols(); ++r2)
+				prod[r1*other.col+r2] += (m[r1*col+c] * other.m[c*other.col+r2]).expand();
+		}
+	}
+	return matrix(row, other.col, prod);
+}
+
+
+/** Product of matrix and scalar. */
+matrix matrix::mul(const numeric & other) const
+{
+	exvector prod(row * col);
+
+	for (unsigned r=0; r<row; ++r)
+		for (unsigned c=0; c<col; ++c)
+			prod[r*col+c] = m[r*col+c] * other;
+
+	return matrix(row, col, prod);
 }
 
 
 /** operator() to access elements.
  *
  *  @param ro row of element
- *  @param co column of element 
+ *  @param co column of element
  *  @exception range_error (index out of range) */
 const ex & matrix::operator() (unsigned ro, unsigned co) const
 {
-    if (ro<0 || ro>=row || co<0 || co>=col)
-        throw (std::range_error("matrix::operator(): index out of range"));
-    
-    return m[ro*col+co];
+	if (ro>=row || co>=col)
+		throw (std::range_error("matrix::operator(): index out of range"));
+
+	return m[ro*col+co];
 }
 
 
@@ -413,12 +634,12 @@ const ex & matrix::operator() (unsigned ro, unsigned co) const
  *  @exception range_error (index out of range) */
 matrix & matrix::set(unsigned ro, unsigned co, ex value)
 {
-    if (ro<0 || ro>=row || co<0 || co>=col)
-        throw (std::range_error("matrix::set(): index out of range"));
+	if (ro>=row || co>=col)
+		throw (std::range_error("matrix::set(): index out of range"));
     
-    ensure_if_modifiable();
-    m[ro*col+co] = value;
-    return *this;
+	ensure_if_modifiable();
+	m[ro*col+co] = value;
+	return *this;
 }
 
 
@@ -426,19 +647,19 @@ matrix & matrix::set(unsigned ro, unsigned co, ex value)
  *  represents the transposed. */
 matrix matrix::transpose(void) const
 {
-    exvector trans(col*row);
-    
-    for (unsigned r=0; r<col; ++r)
-        for (unsigned c=0; c<row; ++c)
-            trans[r*row+c] = m[c*col+r];
-    
-    return matrix(col,row,trans);
+	exvector trans(this->cols()*this->rows());
+	
+	for (unsigned r=0; r<this->cols(); ++r)
+		for (unsigned c=0; c<this->rows(); ++c)
+			trans[r*this->rows()+c] = m[c*this->cols()+r];
+	
+	return matrix(this->cols(),this->rows(),trans);
 }
 
 
 /** Determinant of square matrix.  This routine doesn't actually calculate the
  *  determinant, it only implements some heuristics about which algorithm to
- *  call.  If all the elements of the matrix are elements of an integral domain
+ *  run.  If all the elements of the matrix are elements of an integral domain
  *  the determinant is also in that integral domain and the result is expanded
  *  only.  If one or more elements are from a quotient field the determinant is
  *  usually also in that quotient field and the result is normalized before it
@@ -446,72 +667,127 @@ matrix matrix::transpose(void) const
  *  [[a/(a-b),1],[b/(a-b),1]] is returned as unity.  (In this respect, it
  *  behaves like MapleV and unlike Mathematica.)
  *
+ *  @param     algo allows to chose an algorithm
  *  @return    the determinant as a new expression
- *  @exception logic_error (matrix not square) */
-ex matrix::determinant(void) const
+ *  @exception logic_error (matrix not square)
+ *  @see       determinant_algo */
+ex matrix::determinant(unsigned algo) const
 {
-    if (row!=col)
-        throw (std::logic_error("matrix::determinant(): matrix not square"));
-    GINAC_ASSERT(row*col==m.capacity());
-    if (this->row==1)  // continuation would be pointless
-        return m[0];
-    
-    bool numeric_flag = true;
-    bool normal_flag = false;
-    unsigned sparse_count = 0;  // count non-zero elements
-    for (exvector::const_iterator r=m.begin(); r!=m.end(); ++r) {
-        if (!(*r).is_zero()) {
-            ++sparse_count;
-        }
-        if (!(*r).info(info_flags::numeric)) {
-            numeric_flag = false;
-        }
-        if ((*r).info(info_flags::rational_function) &&
-            !(*r).info(info_flags::crational_polynomial)) {
-            normal_flag = true;
-        }
-    }
-    
-    if (numeric_flag)  // purely numeric matrix
-        return determinant_numeric();
-    
-    // Does anybody really know when a matrix is sparse?
-    if (4*sparse_count<row*col) {  // < row/2 nonzero elements average in a row
-        return determinant_bareiss(normal_flag);
-    }
-    
-    // Now come the minor expansion schemes.  We always develop such that the
-    // smallest minors (i.e, the trivial 1x1 ones) are on the rightmost column.
-    // For this to be efficient it turns out that the emptiest columns (i.e.
-    // the ones with most zeros) should be the ones on the right hand side.
-    // Therefore we presort the columns of the matrix:
-    typedef pair<unsigned,unsigned> uintpair;  // # of zeros, column
-    vector<uintpair> c_zeros;  // number of zeros in column
-    for (unsigned c=0; c<col; ++c) {
-        unsigned acc = 0;
-        for (unsigned r=0; r<row; ++r)
-            if (m[r*col+c].is_zero())
-                ++acc;
-        c_zeros.push_back(uintpair(acc,c));
-    }
-    sort(c_zeros.begin(),c_zeros.end());
-    vector<unsigned> pre_sort;  // unfortunately vector<uintpair> can't be used
-                                // for permutation_sign.
-    for (vector<uintpair>::iterator i=c_zeros.begin(); i!=c_zeros.end(); ++i)
-        pre_sort.push_back(i->second);
-    int sign = permutation_sign(pre_sort);
-    exvector result(row*col);  // represents sorted matrix
-    unsigned c = 0;
-    for (vector<unsigned>::iterator i=pre_sort.begin();
-         i!=pre_sort.end();
-         ++i,++c) {
-        for (unsigned r=0; r<row; ++r)
-            result[r*col+c] = m[r*col+(*i)];
-    }
-    
-    if (normal_flag)
-        return sign*matrix(row,col,result).determinant_minor().normal();
-    return sign*matrix(row,col,result).determinant_minor();
+	if (row!=col)
+		throw (std::logic_error("matrix::determinant(): matrix not square"));
+	GINAC_ASSERT(row*col==m.capacity());
+	
+	// Gather some statistical information about this matrix:
+	bool numeric_flag = true;
+	bool normal_flag = false;
+	unsigned sparse_count = 0;  // counts non-zero elements
+	for (exvector::const_iterator r=m.begin(); r!=m.end(); ++r) {
+		lst srl;  // symbol replacement list
+		ex rtest = (*r).to_rational(srl);
+		if (!rtest.is_zero())
+			++sparse_count;
+		if (!rtest.info(info_flags::numeric))
+			numeric_flag = false;
+		if (!rtest.info(info_flags::crational_polynomial) &&
+			 rtest.info(info_flags::rational_function))
+			normal_flag = true;
+	}
+	
+	// Here is the heuristics in case this routine has to decide:
+	if (algo == determinant_algo::automatic) {
+		// Minor expansion is generally a good guess:
+		algo = determinant_algo::laplace;
+		// Does anybody know when a matrix is really sparse?
+		// Maybe <~row/2.236 nonzero elements average in a row?
+		if (row>3 && 5*sparse_count<=row*col)
+			algo = determinant_algo::bareiss;
+		// Purely numeric matrix can be handled by Gauss elimination.
+		// This overrides any prior decisions.
+		if (numeric_flag)
+			algo = determinant_algo::gauss;
+	}
+	
+	// Trap the trivial case here, since some algorithms don't like it
+	if (this->row==1) {
+		// for consistency with non-trivial determinants...
+		if (normal_flag)
+			return m[0].normal();
+		else
+			return m[0].expand();
+	}
+	
+	// Compute the determinant
+	switch(algo) {
+		case determinant_algo::gauss: {
+			ex det = 1;
+			matrix tmp(*this);
+			int sign = tmp.gauss_elimination(true);
+			for (unsigned d=0; d<row; ++d)
+				det *= tmp.m[d*col+d];
+			if (normal_flag)
+				return (sign*det).normal();
+			else
+				return (sign*det).normal().expand();
+		}
+		case determinant_algo::bareiss: {
+			matrix tmp(*this);
+			int sign;
+			sign = tmp.fraction_free_elimination(true);
+			if (normal_flag)
+				return (sign*tmp.m[row*col-1]).normal();
+			else
+				return (sign*tmp.m[row*col-1]).expand();
+		}
+		case determinant_algo::divfree: {
+			matrix tmp(*this);
+			int sign;
+			sign = tmp.division_free_elimination(true);
+			if (sign==0)
+				return _ex0();
+			ex det = tmp.m[row*col-1];
+			// factor out accumulated bogus slag
+			for (unsigned d=0; d<row-2; ++d)
+				for (unsigned j=0; j<row-d-2; ++j)
+					det = (det/tmp.m[d*col+d]).normal();
+			return (sign*det);
+		}
+		case determinant_algo::laplace:
+		default: {
+			// This is the minor expansion scheme.  We always develop such
+			// that the smallest minors (i.e, the trivial 1x1 ones) are on the
+			// rightmost column.  For this to be efficient it turns out that
+			// the emptiest columns (i.e. the ones with most zeros) should be
+			// the ones on the right hand side.  Therefore we presort the
+			// columns of the matrix:
+			typedef std::pair<unsigned,unsigned> uintpair;
+			std::vector<uintpair> c_zeros;  // number of zeros in column
+			for (unsigned c=0; c<col; ++c) {
+				unsigned acc = 0;
+				for (unsigned r=0; r<row; ++r)
+					if (m[r*col+c].is_zero())
+						++acc;
+				c_zeros.push_back(uintpair(acc,c));
+			}
+			sort(c_zeros.begin(),c_zeros.end());
+			std::vector<unsigned> pre_sort;
+			for (std::vector<uintpair>::iterator i=c_zeros.begin(); i!=c_zeros.end(); ++i)
+				pre_sort.push_back(i->second);
+			int sign = permutation_sign(pre_sort);
+			exvector result(row*col);  // represents sorted matrix
+			unsigned c = 0;
+			for (std::vector<unsigned>::iterator i=pre_sort.begin();
+				 i!=pre_sort.end();
+				 ++i,++c) {
+				for (unsigned r=0; r<row; ++r)
+					result[r*col+c] = m[r*col+(*i)];
+			}
+			
+			if (normal_flag)
+				return (sign*matrix(row,col,result).determinant_minor()).normal();
+			else
+				return sign*matrix(row,col,result).determinant_minor();
+		}
+	}
 }
 
 
@@ -523,19 +799,18 @@ ex matrix::determinant(void) const
  *  @exception logic_error (matrix not square) */
 ex matrix::trace(void) const
 {
-    if (row != col)
-        throw (std::logic_error("matrix::trace(): matrix not square"));
-    GINAC_ASSERT(row*col==m.capacity());
-    
-    ex tr;
-    for (unsigned r=0; r<col; ++r)
-        tr += m[r*col+r];
-    
-    if (tr.info(info_flags::rational_function) &&
-        !tr.info(info_flags::crational_polynomial))
-        return tr.normal();
-    else
-        return tr.expand();
+	if (row != col)
+		throw (std::logic_error("matrix::trace(): matrix not square"));
+	
+	ex tr;
+	for (unsigned r=0; r<col; ++r)
+		tr += m[r*col+r];
+	
+	if (tr.info(info_flags::rational_function) &&
+		!tr.info(info_flags::crational_polynomial))
+		return tr.normal();
+	else
+		return tr.expand();
 }
 
 
@@ -552,41 +827,41 @@ ex matrix::trace(void) const
  *  @see       matrix::determinant() */
 ex matrix::charpoly(const symbol & lambda) const
 {
-    if (row != col)
-        throw (std::logic_error("matrix::charpoly(): matrix not square"));
-    
-    bool numeric_flag = true;
-    for (exvector::const_iterator r=m.begin(); r!=m.end(); ++r) {
-        if (!(*r).info(info_flags::numeric)) {
-            numeric_flag = false;
-        }
-    }
-    
-    // The pure numeric case is traditionally rather common.  Hence, it is
-    // trapped and we use Leverrier's algorithm which goes as row^3 for
-    // every coefficient.  The expensive section is the matrix multiplication.
-    if (numeric_flag) {
-        matrix B(*this);
-        ex c = B.trace();
-        ex poly = power(lambda,row)-c*power(lambda,row-1);
-        for (unsigned i=1; i<row; ++i) {
-            for (unsigned j=0; j<row; ++j)
-                B.m[j*col+j] -= c;
-            B = this->mul(B);
-            c = B.trace()/ex(i+1);
-            poly -= c*power(lambda,row-i-1);
-        }
-        if (row%2)
-            return -poly;
-        else
-            return poly;
-    }
-    
-    matrix M(*this);
-    for (unsigned r=0; r<col; ++r)
-        M.m[r*col+r] -= lambda;
-    
-    return M.determinant().collect(lambda);
+	if (row != col)
+		throw (std::logic_error("matrix::charpoly(): matrix not square"));
+	
+	bool numeric_flag = true;
+	for (exvector::const_iterator r=m.begin(); r!=m.end(); ++r) {
+		if (!(*r).info(info_flags::numeric)) {
+			numeric_flag = false;
+		}
+	}
+	
+	// The pure numeric case is traditionally rather common.  Hence, it is
+	// trapped and we use Leverrier's algorithm which goes as row^3 for
+	// every coefficient.  The expensive part is the matrix multiplication.
+	if (numeric_flag) {
+		matrix B(*this);
+		ex c = B.trace();
+		ex poly = power(lambda,row)-c*power(lambda,row-1);
+		for (unsigned i=1; i<row; ++i) {
+			for (unsigned j=0; j<row; ++j)
+				B.m[j*col+j] -= c;
+			B = this->mul(B);
+			c = B.trace()/ex(i+1);
+			poly -= c*power(lambda,row-i-1);
+		}
+		if (row%2)
+			return -poly;
+		else
+			return poly;
+	}
+	
+	matrix M(*this);
+	for (unsigned r=0; r<col; ++r)
+		M.m[r*col+r] -= lambda;
+	
+	return M.determinant().collect(lambda);
 }
 
 
@@ -597,305 +872,144 @@ ex matrix::charpoly(const symbol & lambda) const
  *  @exception runtime_error (singular matrix) */
 matrix matrix::inverse(void) const
 {
-    if (row != col)
-        throw (std::logic_error("matrix::inverse(): matrix not square"));
-    
-    matrix tmp(row,col);
-    // set tmp to the unit matrix
-    for (unsigned i=0; i<col; ++i)
-        tmp.m[i*col+i] = _ex1();
-
-    // create a copy of this matrix
-    matrix cpy(*this);
-    for (unsigned r1=0; r1<row; ++r1) {
-        int indx = cpy.pivot(r1);
-        if (indx == -1) {
-            throw (std::runtime_error("matrix::inverse(): singular matrix"));
-        }
-        if (indx != 0) {  // swap rows r and indx of matrix tmp
-            for (unsigned i=0; i<col; ++i) {
-                tmp.m[r1*col+i].swap(tmp.m[indx*col+i]);
-            }
-        }
-        ex a1 = cpy.m[r1*col+r1];
-        for (unsigned c=0; c<col; ++c) {
-            cpy.m[r1*col+c] /= a1;
-            tmp.m[r1*col+c] /= a1;
-        }
-        for (unsigned r2=0; r2<row; ++r2) {
-            if (r2 != r1) {
-                ex a2 = cpy.m[r2*col+r1];
-                for (unsigned c=0; c<col; ++c) {
-                    cpy.m[r2*col+c] -= a2 * cpy.m[r1*col+c];
-                    tmp.m[r2*col+c] -= a2 * tmp.m[r1*col+c];
-                }
-            }
-        }
-    }
-    return tmp;
+	if (row != col)
+		throw (std::logic_error("matrix::inverse(): matrix not square"));
+	
+	// This routine actually doesn't do anything fancy at all.  We compute the
+	// inverse of the matrix A by solving the system A * A^{-1} == Id.
+	
+	// First populate the identity matrix supposed to become the right hand side.
+	matrix identity(row,col);
+	for (unsigned i=0; i<row; ++i)
+		identity.set(i,i,_ex1());
+	
+	// Populate a dummy matrix of variables, just because of compatibility with
+	// matrix::solve() which wants this (for compatibility with under-determined
+	// systems of equations).
+	matrix vars(row,col);
+	for (unsigned r=0; r<row; ++r)
+		for (unsigned c=0; c<col; ++c)
+			vars.set(r,c,symbol());
+	
+	matrix sol(row,col);
+	try {
+		sol = this->solve(vars,identity);
+	} catch (const std::runtime_error & e) {
+	    if (e.what()==std::string("matrix::solve(): inconsistent linear system"))
+			throw (std::runtime_error("matrix::inverse(): singular matrix"));
+		else
+			throw;
+	}
+	return sol;
 }
 
 
-// superfluous helper function
-void matrix::ffe_swap(unsigned r1, unsigned c1, unsigned r2 ,unsigned c2)
-{
-    ensure_if_modifiable();
-    
-    ex tmp = ffe_get(r1,c1);
-    ffe_set(r1,c1,ffe_get(r2,c2));
-    ffe_set(r2,c2,tmp);
-}
-
-// superfluous helper function
-void matrix::ffe_set(unsigned r, unsigned c, ex e)
-{
-    set(r-1,c-1,e);
-}
-
-// superfluous helper function
-ex matrix::ffe_get(unsigned r, unsigned c) const
-{
-    return operator()(r-1,c-1);
-}
-
-/** Solve a set of equations for an m x n matrix by fraction-free Gaussian
- *  elimination.  Based on algorithm 9.1 from 'Algorithms for Computer Algebra'
- *  by Keith O. Geddes et al.
- *
- *  @param vars n x p matrix
- *  @param rhs m x p matrix
- *  @exception logic_error (incompatible matrices)
- *  @exception runtime_error (singular matrix) */
-matrix matrix::fraction_free_elim(const matrix & vars,
-                                  const matrix & rhs) const
-{
-    // FIXME: use implementation of matrix::fraction_free_elim
-    if ((row != rhs.row) || (col != vars.row) || (rhs.col != vars.col))
-        throw (std::logic_error("matrix::fraction_free_elim(): incompatible matrices"));
-    
-    matrix a(*this);  // make a copy of the matrix
-    matrix b(rhs);    // make a copy of the rhs vector
-    
-    // given an m x n matrix a, reduce it to upper echelon form
-    unsigned m = a.row;
-    unsigned n = a.col;
-    int sign = 1;
-    ex divisor = 1;
-    unsigned r = 1;
-    
-    // eliminate below row r, with pivot in column k
-    for (unsigned k=1; (k<=n)&&(r<=m); ++k) {
-        // find a nonzero pivot
-        unsigned p;
-        for (p=r; (p<=m)&&(a.ffe_get(p,k).is_equal(_ex0())); ++p) {}
-        // pivot is in row p
-        if (p<=m) {
-            if (p!=r) {
-                // switch rows p and r
-                for (unsigned j=k; j<=n; ++j)
-                    a.ffe_swap(p,j,r,j);
-                b.ffe_swap(p,1,r,1);
-                // keep track of sign changes due to row exchange
-                sign = -sign;
-            }
-            for (unsigned i=r+1; i<=m; ++i) {
-                for (unsigned j=k+1; j<=n; ++j) {
-                    a.ffe_set(i,j,(a.ffe_get(r,k)*a.ffe_get(i,j)
-                                  -a.ffe_get(r,j)*a.ffe_get(i,k))/divisor);
-                    a.ffe_set(i,j,a.ffe_get(i,j).normal() /*.normal() */ );
-                }
-                b.ffe_set(i,1,(a.ffe_get(r,k)*b.ffe_get(i,1)
-                              -b.ffe_get(r,1)*a.ffe_get(i,k))/divisor);
-                b.ffe_set(i,1,b.ffe_get(i,1).normal() /*.normal() */ );
-                a.ffe_set(i,k,0);
-            }
-            divisor = a.ffe_get(r,k);
-            r++;
-        }
-    }
-    // optionally compute the determinant for square or augmented matrices
-    // if (r==m+1) { det = sign*divisor; } else { det = 0; }
-    
-    /*
-    for (unsigned r=1; r<=m; ++r) {
-        for (unsigned c=1; c<=n; ++c) {
-            cout << a.ffe_get(r,c) << "\t";
-        }
-        cout << " | " <<  b.ffe_get(r,1) << endl;
-    }
-    */
-    
-#ifdef DO_GINAC_ASSERT
-    // test if we really have an upper echelon matrix
-    int zero_in_last_row = -1;
-    for (unsigned r=1; r<=m; ++r) {
-        int zero_in_this_row=0;
-        for (unsigned c=1; c<=n; ++c) {
-            if (a.ffe_get(r,c).is_equal(_ex0()))
-               zero_in_this_row++;
-            else
-                break;
-        }
-        GINAC_ASSERT((zero_in_this_row>zero_in_last_row)||(zero_in_this_row=n));
-        zero_in_last_row = zero_in_this_row;
-    }
-#endif // def DO_GINAC_ASSERT
-    
-    /*
-    cout << "after" << endl;
-    cout << "a=" << a << endl;
-    cout << "b=" << b << endl;
-    */
-    
-    // assemble solution
-    matrix sol(n,1);
-    unsigned last_assigned_sol = n+1;
-    for (unsigned r=m; r>0; --r) {
-        unsigned first_non_zero = 1;
-        while ((first_non_zero<=n)&&(a.ffe_get(r,first_non_zero).is_zero()))
-            first_non_zero++;
-        if (first_non_zero>n) {
-            // row consists only of zeroes, corresponding rhs must be 0 as well
-            if (!b.ffe_get(r,1).is_zero()) {
-                throw (std::runtime_error("matrix::fraction_free_elim(): singular matrix"));
-            }
-        } else {
-            // assign solutions for vars between first_non_zero+1 and
-            // last_assigned_sol-1: free parameters
-            for (unsigned c=first_non_zero+1; c<=last_assigned_sol-1; ++c) {
-                sol.ffe_set(c,1,vars.ffe_get(c,1));
-            }
-            ex e = b.ffe_get(r,1);
-            for (unsigned c=first_non_zero+1; c<=n; ++c) {
-                e=e-a.ffe_get(r,c)*sol.ffe_get(c,1);
-            }
-            sol.ffe_set(first_non_zero,1,
-                        (e/a.ffe_get(r,first_non_zero)).normal());
-            last_assigned_sol = first_non_zero;
-        }
-    }
-    // assign solutions for vars between 1 and
-    // last_assigned_sol-1: free parameters
-    for (unsigned c=1; c<=last_assigned_sol-1; ++c)
-        sol.ffe_set(c,1,vars.ffe_get(c,1));
-    
-#ifdef DO_GINAC_ASSERT
-    // test solution with echelon matrix
-    for (unsigned r=1; r<=m; ++r) {
-        ex e = 0;
-        for (unsigned c=1; c<=n; ++c)
-            e = e+a.ffe_get(r,c)*sol.ffe_get(c,1);
-        if (!(e-b.ffe_get(r,1)).normal().is_zero()) {
-            cout << "e=" << e;
-            cout << "b.ffe_get(" << r<<",1)=" << b.ffe_get(r,1) << endl;
-            cout << "diff=" << (e-b.ffe_get(r,1)).normal() << endl;
-        }
-        GINAC_ASSERT((e-b.ffe_get(r,1)).normal().is_zero());
-    }
-    
-    // test solution with original matrix
-    for (unsigned r=1; r<=m; ++r) {
-        ex e = 0;
-        for (unsigned c=1; c<=n; ++c)
-            e = e+ffe_get(r,c)*sol.ffe_get(c,1);
-        try {
-            if (!(e-rhs.ffe_get(r,1)).normal().is_zero()) {
-                cout << "e=" << e << endl;
-                e.printtree(cout);
-                ex en = e.normal();
-                cout << "e.normal()=" << en << endl;
-                en.printtree(cout);
-                cout << "rhs.ffe_get(" << r<<",1)=" << rhs.ffe_get(r,1) << endl;
-                cout << "diff=" << (e-rhs.ffe_get(r,1)).normal() << endl;
-            }
-        } catch (...) {
-            ex xxx = e - rhs.ffe_get(r,1);
-            cerr << "xxx=" << xxx << endl << endl;
-        }
-        GINAC_ASSERT((e-rhs.ffe_get(r,1)).normal().is_zero());
-    }
-#endif // def DO_GINAC_ASSERT
-    
-    return sol;
-}
-
-/** Solve a set of equations for an m x n matrix.
+/** Solve a linear system consisting of a m x n matrix and a m x p right hand
+ *  side by applying an elimination scheme to the augmented matrix.
  *
- *  @param vars n x p matrix
+ *  @param vars n x p matrix, all elements must be symbols 
  *  @param rhs m x p matrix
+ *  @return n x p solution matrix
  *  @exception logic_error (incompatible matrices)
- *  @exception runtime_error (singular matrix) */
+ *  @exception invalid_argument (1st argument must be matrix of symbols)
+ *  @exception runtime_error (inconsistent linear system)
+ *  @see       solve_algo */
 matrix matrix::solve(const matrix & vars,
-                     const matrix & rhs) const
+					 const matrix & rhs,
+					 unsigned algo) const
 {
-    if ((row != rhs.row) || (col != vars.row) || (rhs.col != vars.col))
-        throw (std::logic_error("matrix::solve(): incompatible matrices"));
-    
-    throw (std::runtime_error("FIXME: need implementation."));
-}
-
-/** Old and obsolete interface: */
-matrix matrix::old_solve(const matrix & v) const
-{
-    if ((v.row != col) || (col != v.row))
-        throw (std::logic_error("matrix::solve(): incompatible matrices"));
-    
-    // build the augmented matrix of *this with v attached to the right
-    matrix tmp(row,col+v.col);
-    for (unsigned r=0; r<row; ++r) {
-        for (unsigned c=0; c<col; ++c)
-            tmp.m[r*tmp.col+c] = this->m[r*col+c];
-        for (unsigned c=0; c<v.col; ++c)
-            tmp.m[r*tmp.col+c+col] = v.m[r*v.col+c];
-    }
-    // cout << "augmented: " << tmp << endl;
-    tmp.gauss_elimination();
-    // cout << "degaussed: " << tmp << endl;
-    // assemble the solution matrix
-    exvector sol(v.row*v.col);
-    for (unsigned c=0; c<v.col; ++c) {
-        for (unsigned r=row; r>0; --r) {
-            for (unsigned i=r; i<col; ++i)
-                sol[(r-1)*v.col+c] -= tmp.m[(r-1)*tmp.col+i]*sol[i*v.col+c];
-            sol[(r-1)*v.col+c] += tmp.m[(r-1)*tmp.col+col+c];
-            sol[(r-1)*v.col+c] = (sol[(r-1)*v.col+c]/tmp.m[(r-1)*tmp.col+(r-1)]).normal();
-        }
-    }
-    return matrix(v.row, v.col, sol);
+	const unsigned m = this->rows();
+	const unsigned n = this->cols();
+	const unsigned p = rhs.cols();
+	
+	// syntax checks    
+	if ((rhs.rows() != m) || (vars.rows() != n) || (vars.col != p))
+		throw (std::logic_error("matrix::solve(): incompatible matrices"));
+	for (unsigned ro=0; ro<n; ++ro)
+		for (unsigned co=0; co<p; ++co)
+			if (!vars(ro,co).info(info_flags::symbol))
+				throw (std::invalid_argument("matrix::solve(): 1st argument must be matrix of symbols"));
+	
+	// build the augmented matrix of *this with rhs attached to the right
+	matrix aug(m,n+p);
+	for (unsigned r=0; r<m; ++r) {
+		for (unsigned c=0; c<n; ++c)
+			aug.m[r*(n+p)+c] = this->m[r*n+c];
+		for (unsigned c=0; c<p; ++c)
+			aug.m[r*(n+p)+c+n] = rhs.m[r*p+c];
+	}
+	
+	// Gather some statistical information about the augmented matrix:
+	bool numeric_flag = true;
+	for (exvector::const_iterator r=aug.m.begin(); r!=aug.m.end(); ++r) {
+		if (!(*r).info(info_flags::numeric))
+			numeric_flag = false;
+	}
+	
+	// Here is the heuristics in case this routine has to decide:
+	if (algo == solve_algo::automatic) {
+		// Bareiss (fraction-free) elimination is generally a good guess:
+		algo = solve_algo::bareiss;
+		// For m<3, Bareiss elimination is equivalent to division free
+		// elimination but has more logistic overhead
+		if (m<3)
+			algo = solve_algo::divfree;
+		// This overrides any prior decisions.
+		if (numeric_flag)
+			algo = solve_algo::gauss;
+	}
+	
+	// Eliminate the augmented matrix:
+	switch(algo) {
+		case solve_algo::gauss:
+			aug.gauss_elimination();
+			break;
+		case solve_algo::divfree:
+			aug.division_free_elimination();
+			break;
+		case solve_algo::bareiss:
+		default:
+			aug.fraction_free_elimination();
+	}
+	
+	// assemble the solution matrix:
+	matrix sol(n,p);
+	for (unsigned co=0; co<p; ++co) {
+		unsigned last_assigned_sol = n+1;
+		for (int r=m-1; r>=0; --r) {
+			unsigned fnz = 1;    // first non-zero in row
+			while ((fnz<=n) && (aug.m[r*(n+p)+(fnz-1)].is_zero()))
+				++fnz;
+			if (fnz>n) {
+				// row consists only of zeros, corresponding rhs must be 0, too
+				if (!aug.m[r*(n+p)+n+co].is_zero()) {
+					throw (std::runtime_error("matrix::solve(): inconsistent linear system"));
+				}
+			} else {
+				// assign solutions for vars between fnz+1 and
+				// last_assigned_sol-1: free parameters
+				for (unsigned c=fnz; c<last_assigned_sol-1; ++c)
+					sol.set(c,co,vars.m[c*p+co]);
+				ex e = aug.m[r*(n+p)+n+co];
+				for (unsigned c=fnz; c<n; ++c)
+					e -= aug.m[r*(n+p)+c]*sol.m[c*p+co];
+				sol.set(fnz-1,co,
+						(e/(aug.m[r*(n+p)+(fnz-1)])).normal());
+				last_assigned_sol = fnz;
+			}
+		}
+		// assign solutions for vars between 1 and
+		// last_assigned_sol-1: free parameters
+		for (unsigned ro=0; ro<last_assigned_sol-1; ++ro)
+			sol.set(ro,co,vars(ro,co));
+	}
+	
+	return sol;
 }
 
 
 // protected
 
-/** Determinant of purely numeric matrix, using pivoting.
- *
- *  @see       matrix::determinant() */
-ex matrix::determinant_numeric(void) const
-{
-    matrix tmp(*this);
-    ex det = _ex1();
-    ex piv;
-    
-    // standard Gauss method:
-    for (unsigned r1=0; r1<row; ++r1) {
-        int indx = tmp.pivot(r1);
-        if (indx == -1)
-            return _ex0();
-        if (indx != 0)
-            det *= _ex_1();
-        det = det * tmp.m[r1*col+r1];
-        for (unsigned r2=r1+1; r2<row; ++r2) {
-            piv = tmp.m[r2*col+r1] / tmp.m[r1*col+r1];
-            for (unsigned c=r1+1; c<col; c++) {
-                tmp.m[r2*col+c] -= piv * tmp.m[r1*col+c];
-            }
-        }
-    }
-    
-    return det;
-}
-
-
 /** Recursive determinant for small matrices having at least one symbolic
  *  entry.  The basic algorithm, known as Laplace-expansion, is enhanced by
  *  some bookkeeping to avoid calculation of the same submatrices ("minors")
@@ -908,379 +1022,396 @@ ex matrix::determinant_numeric(void) const
  *  @see matrix::determinant() */
 ex matrix::determinant_minor(void) const
 {
-    // for small matrices the algorithm does not make any sense:
-    if (this->row==1)
-        return m[0];
-    if (this->row==2)
-        return (m[0]*m[3]-m[2]*m[1]).expand();
-    if (this->row==3)
-        return (m[0]*m[4]*m[8]-m[0]*m[5]*m[7]-
-                m[1]*m[3]*m[8]+m[2]*m[3]*m[7]+
-                m[1]*m[5]*m[6]-m[2]*m[4]*m[6]).expand();
-    
-    // This algorithm can best be understood by looking at a naive
-    // implementation of Laplace-expansion, like this one:
-    // ex det;
-    // matrix minorM(this->row-1,this->col-1);
-    // for (unsigned r1=0; r1<this->row; ++r1) {
-    //     // shortcut if element(r1,0) vanishes
-    //     if (m[r1*col].is_zero())
-    //         continue;
-    //     // assemble the minor matrix
-    //     for (unsigned r=0; r<minorM.rows(); ++r) {
-    //         for (unsigned c=0; c<minorM.cols(); ++c) {
-    //             if (r<r1)
-    //                 minorM.set(r,c,m[r*col+c+1]);
-    //             else
-    //                 minorM.set(r,c,m[(r+1)*col+c+1]);
-    //         }
-    //     }
-    //     // recurse down and care for sign:
-    //     if (r1%2)
-    //         det -= m[r1*col] * minorM.determinant_minor();
-    //     else
-    //         det += m[r1*col] * minorM.determinant_minor();
-    // }
-    // return det.expand();
-    // What happens is that while proceeding down many of the minors are
-    // computed more than once.  In particular, there are binomial(n,k)
-    // kxk minors and each one is computed factorial(n-k) times.  Therefore
-    // it is reasonable to store the results of the minors.  We proceed from
-    // right to left.  At each column c we only need to retrieve the minors
-    // calculated in step c-1.  We therefore only have to store at most 
-    // 2*binomial(n,n/2) minors.
-    
-    // Unique flipper counter for partitioning into minors
-    vector<unsigned> Pkey;
-    Pkey.reserve(this->col);
-    // key for minor determinant (a subpartition of Pkey)
-    vector<unsigned> Mkey;
-    Mkey.reserve(this->col-1);
-    // we store our subminors in maps, keys being the rows they arise from
-    typedef map<vector<unsigned>,class ex> Rmap;
-    typedef map<vector<unsigned>,class ex>::value_type Rmap_value;
-    Rmap A;
-    Rmap B;
-    ex det;
-    // initialize A with last column:
-    for (unsigned r=0; r<this->col; ++r) {
-        Pkey.erase(Pkey.begin(),Pkey.end());
-        Pkey.push_back(r);
-        A.insert(Rmap_value(Pkey,m[this->col*r+this->col-1]));
-    }
-    // proceed from right to left through matrix
-    for (int c=this->col-2; c>=0; --c) {
-        Pkey.erase(Pkey.begin(),Pkey.end());  // don't change capacity
-        Mkey.erase(Mkey.begin(),Mkey.end());
-        for (unsigned i=0; i<this->col-c; ++i)
-            Pkey.push_back(i);
-        unsigned fc = 0;  // controls logic for our strange flipper counter
-        do {
-            det = _ex0();
-            for (unsigned r=0; r<this->col-c; ++r) {
-                // maybe there is nothing to do?
-                if (m[Pkey[r]*this->col+c].is_zero())
-                    continue;
-                // create the sorted key for all possible minors
-                Mkey.erase(Mkey.begin(),Mkey.end());
-                for (unsigned i=0; i<this->col-c; ++i)
-                    if (i!=r)
-                        Mkey.push_back(Pkey[i]);
-                // Fetch the minors and compute the new determinant
-                if (r%2)
-                    det -= m[Pkey[r]*this->col+c]*A[Mkey];
-                else
-                    det += m[Pkey[r]*this->col+c]*A[Mkey];
-            }
-            // prevent build-up of deep nesting of expressions saves time:
-            det = det.expand();
-            // store the new determinant at its place in B:
-            if (!det.is_zero())
-                B.insert(Rmap_value(Pkey,det));
-            // increment our strange flipper counter
-            for (fc=this->col-c; fc>0; --fc) {
-                ++Pkey[fc-1];
-                if (Pkey[fc-1]<fc+c)
-                    break;
-            }
-            if (fc<this->col-c)
-                for (unsigned j=fc; j<this->col-c; ++j)
-                    Pkey[j] = Pkey[j-1]+1;
-        } while(fc);
-        // next column, so change the role of A and B:
-        A = B;
-        B.clear();
-    }
-    
-    return det;
-}
-
-/** Helper function to divide rational functions, as needed in any Bareiss
- *  elimination scheme over a quotient field.
- *  
- *  @see divide() */
-bool rat_divide(const ex & a, const ex & b, ex & q, bool check_args = true)
-{
-    q = _ex0();
-    if (b.is_zero())
-        throw(std::overflow_error("rat_divide(): division by zero"));
-    if (a.is_zero())
-        return true;
-    if (is_ex_exactly_of_type(b, numeric)) {
-        q = a / b;
-        return true;
-    } else if (is_ex_exactly_of_type(a, numeric))
-        return false;
-    ex a_n = a.numer();
-    ex a_d = a.denom();
-    ex b_n = b.numer();
-    ex b_d = b.denom();
-    ex n;  // new numerator
-    ex d;  // new denominator
-    bool check = true;
-    check &= divide(a_n, b_n, n, check_args);
-    check &= divide(a_d, b_d, d, check_args);
-    q = n/d;
-    return check;
-}
-
-
-/** Determinant computed by using fraction free elimination.  This
- *  routine is only called internally by matrix::determinant().
- *
- *  @param normalize may be set to false only in integral domains. */
-ex matrix::determinant_bareiss(bool normalize) const
-{
-    if (rows()==1)
-        return m[0];
-    
-    int sign = 1;
-    ex divisor = 1;
-    ex dividend;
-    
-    // we populate a tmp matrix to subsequently operate on, it should
-    // be normalized even though this algorithm doesn't need GCDs since
-    // the elements of *this might be unnormalized, which complicates
-    // things:
-    matrix tmp(*this);
-    exvector::const_iterator i = m.begin();
-    exvector::iterator ti = tmp.m.begin();
-    for (; i!= m.end(); ++i, ++ti) {
-        if (normalize)
-            (*ti) = (*i).normal();
-        else
-            (*ti) = (*i);
-    }
-    
-    for (unsigned r1=0; r1<row-1; ++r1) {
-        int indx = tmp.pivot(r1);
-        if (indx==-1)
-            return _ex0();
-        if (indx>0)
-            sign = -sign;
-        if (r1>0) {
-            divisor = tmp.m[(r1-1)*col+(r1-1)].expand();
-            // delete the elements we don't need anymore:
-            for (unsigned c=0; c<col; ++c)
-                tmp.m[(r1-1)*col+c] = _ex0();
-        }
-        for (unsigned r2=r1+1; r2<row; ++r2) {
-            for (unsigned c=r1+1; c<col; ++c) {
-                lst srl;  // symbol replacement list for .to_rational()
-                dividend = (tmp.m[r1*tmp.col+r1]*tmp.m[r2*tmp.col+c]
-                           -tmp.m[r2*tmp.col+r1]*tmp.m[r1*tmp.col+c]).expand();
-                if (normalize) {
-#ifdef DO_GINAC_ASSERT
-                    GINAC_ASSERT(rat_divide(dividend.to_rational(srl),
-                                            divisor.to_rational(srl),
-                                            tmp.m[r2*tmp.col+c],true));
-#else
-                    rat_divide(dividend.to_rational(srl),
-                               divisor.to_rational(srl),
-                               tmp.m[r2*tmp.col+c],false);
-#endif                    
-                }
-                else {
-#ifdef DO_GINAC_ASSERT
-                    GINAC_ASSERT(divide(dividend.to_rational(srl),
-                                        divisor.to_rational(srl),
-                                        tmp.m[r2*tmp.col+c],true));
-#else
-                    divide(dividend.to_rational(srl),
-                           divisor.to_rational(srl),
-                           tmp.m[r2*tmp.col+c],false);
-#endif                    
-                }
-                tmp.m[r2*tmp.col+c] = tmp.m[r2*tmp.col+c].subs(srl);
-            }
-            for (unsigned c=0; c<=r1; ++c)
-                tmp.m[r2*tmp.col+c] = _ex0();
-        }
-    }
-    
-    return sign*tmp.m[tmp.row*tmp.col-1];
+	// for small matrices the algorithm does not make any sense:
+	const unsigned n = this->cols();
+	if (n==1)
+		return m[0].expand();
+	if (n==2)
+		return (m[0]*m[3]-m[2]*m[1]).expand();
+	if (n==3)
+		return (m[0]*m[4]*m[8]-m[0]*m[5]*m[7]-
+		        m[1]*m[3]*m[8]+m[2]*m[3]*m[7]+
+		        m[1]*m[5]*m[6]-m[2]*m[4]*m[6]).expand();
+	
+	// This algorithm can best be understood by looking at a naive
+	// implementation of Laplace-expansion, like this one:
+	// ex det;
+	// matrix minorM(this->rows()-1,this->cols()-1);
+	// for (unsigned r1=0; r1<this->rows(); ++r1) {
+	//     // shortcut if element(r1,0) vanishes
+	//     if (m[r1*col].is_zero())
+	//         continue;
+	//     // assemble the minor matrix
+	//     for (unsigned r=0; r<minorM.rows(); ++r) {
+	//         for (unsigned c=0; c<minorM.cols(); ++c) {
+	//             if (r<r1)
+	//                 minorM.set(r,c,m[r*col+c+1]);
+	//             else
+	//                 minorM.set(r,c,m[(r+1)*col+c+1]);
+	//         }
+	//     }
+	//     // recurse down and care for sign:
+	//     if (r1%2)
+	//         det -= m[r1*col] * minorM.determinant_minor();
+	//     else
+	//         det += m[r1*col] * minorM.determinant_minor();
+	// }
+	// return det.expand();
+	// What happens is that while proceeding down many of the minors are
+	// computed more than once.  In particular, there are binomial(n,k)
+	// kxk minors and each one is computed factorial(n-k) times.  Therefore
+	// it is reasonable to store the results of the minors.  We proceed from
+	// right to left.  At each column c we only need to retrieve the minors
+	// calculated in step c-1.  We therefore only have to store at most 
+	// 2*binomial(n,n/2) minors.
+	
+	// Unique flipper counter for partitioning into minors
+	std::vector<unsigned> Pkey;
+	Pkey.reserve(n);
+	// key for minor determinant (a subpartition of Pkey)
+	std::vector<unsigned> Mkey;
+	Mkey.reserve(n-1);
+	// we store our subminors in maps, keys being the rows they arise from
+	typedef std::map<std::vector<unsigned>,class ex> Rmap;
+	typedef std::map<std::vector<unsigned>,class ex>::value_type Rmap_value;
+	Rmap A;
+	Rmap B;
+	ex det;
+	// initialize A with last column:
+	for (unsigned r=0; r<n; ++r) {
+		Pkey.erase(Pkey.begin(),Pkey.end());
+		Pkey.push_back(r);
+		A.insert(Rmap_value(Pkey,m[n*(r+1)-1]));
+	}
+	// proceed from right to left through matrix
+	for (int c=n-2; c>=0; --c) {
+		Pkey.erase(Pkey.begin(),Pkey.end());  // don't change capacity
+		Mkey.erase(Mkey.begin(),Mkey.end());
+		for (unsigned i=0; i<n-c; ++i)
+			Pkey.push_back(i);
+		unsigned fc = 0;  // controls logic for our strange flipper counter
+		do {
+			det = _ex0();
+			for (unsigned r=0; r<n-c; ++r) {
+				// maybe there is nothing to do?
+				if (m[Pkey[r]*n+c].is_zero())
+					continue;
+				// create the sorted key for all possible minors
+				Mkey.erase(Mkey.begin(),Mkey.end());
+				for (unsigned i=0; i<n-c; ++i)
+					if (i!=r)
+						Mkey.push_back(Pkey[i]);
+				// Fetch the minors and compute the new determinant
+				if (r%2)
+					det -= m[Pkey[r]*n+c]*A[Mkey];
+				else
+					det += m[Pkey[r]*n+c]*A[Mkey];
+			}
+			// prevent build-up of deep nesting of expressions saves time:
+			det = det.expand();
+			// store the new determinant at its place in B:
+			if (!det.is_zero())
+				B.insert(Rmap_value(Pkey,det));
+			// increment our strange flipper counter
+			for (fc=n-c; fc>0; --fc) {
+				++Pkey[fc-1];
+				if (Pkey[fc-1]<fc+c)
+					break;
+			}
+			if (fc<n-c && fc>0)
+				for (unsigned j=fc; j<n-c; ++j)
+					Pkey[j] = Pkey[j-1]+1;
+		} while(fc);
+		// next column, so change the role of A and B:
+		A = B;
+		B.clear();
+	}
+	
+	return det;
 }
 
 
-/** Perform the steps of an ordinary Gaussian elimination to bring the matrix
- *  into an upper echelon form.
+/** Perform the steps of an ordinary Gaussian elimination to bring the m x n
+ *  matrix into an upper echelon form.  The algorithm is ok for matrices
+ *  with numeric coefficients but quite unsuited for symbolic matrices.
  *
+ *  @param det may be set to true to save a lot of space if one is only
+ *  interested in the diagonal elements (i.e. for calculating determinants).
+ *  The others are set to zero in this case.
  *  @return sign is 1 if an even number of rows was swapped, -1 if an odd
  *  number of rows was swapped and 0 if the matrix is singular. */
-int matrix::gauss_elimination(void)
+int matrix::gauss_elimination(const bool det)
 {
-    int sign = 1;
-    ensure_if_modifiable();
-    for (unsigned r1=0; r1<row-1; ++r1) {
-        int indx = pivot(r1);
-        if (indx == -1)
-            return 0;  // Note: leaves *this in a messy state.
-        if (indx > 0)
-            sign = -sign;
-        for (unsigned r2=r1+1; r2<row; ++r2) {
-            for (unsigned c=r1+1; c<col; ++c)
-                this->m[r2*col+c] -= this->m[r2*col+r1]*this->m[r1*col+c]/this->m[r1*col+r1];
-            for (unsigned c=0; c<=r1; ++c)
-                this->m[r2*col+c] = _ex0();
-        }
-    }
-    
-    return sign;
+	ensure_if_modifiable();
+	const unsigned m = this->rows();
+	const unsigned n = this->cols();
+	GINAC_ASSERT(!det || n==m);
+	int sign = 1;
+	
+	unsigned r0 = 0;
+	for (unsigned r1=0; (r1<n-1)&&(r0<m-1); ++r1) {
+		int indx = pivot(r0, r1, true);
+		if (indx == -1) {
+			sign = 0;
+			if (det)
+				return 0;  // leaves *this in a messy state
+		}
+		if (indx>=0) {
+			if (indx > 0)
+				sign = -sign;
+			for (unsigned r2=r0+1; r2<m; ++r2) {
+				if (!this->m[r2*n+r1].is_zero()) {
+					// yes, there is something to do in this row
+					ex piv = this->m[r2*n+r1] / this->m[r0*n+r1];
+					for (unsigned c=r1+1; c<n; ++c) {
+						this->m[r2*n+c] -= piv * this->m[r0*n+c];
+						if (!this->m[r2*n+c].info(info_flags::numeric))
+							this->m[r2*n+c] = this->m[r2*n+c].normal();
+					}
+				}
+				// fill up left hand side with zeros
+				for (unsigned c=0; c<=r1; ++c)
+					this->m[r2*n+c] = _ex0();
+			}
+			if (det) {
+				// save space by deleting no longer needed elements
+				for (unsigned c=r0+1; c<n; ++c)
+					this->m[r0*n+c] = _ex0();
+			}
+			++r0;
+		}
+	}
+	
+	return sign;
 }
 
 
-/** Perform the steps of division free elimination to bring the matrix
+/** Perform the steps of division free elimination to bring the m x n matrix
  *  into an upper echelon form.
  *
+ *  @param det may be set to true to save a lot of space if one is only
+ *  interested in the diagonal elements (i.e. for calculating determinants).
+ *  The others are set to zero in this case.
  *  @return sign is 1 if an even number of rows was swapped, -1 if an odd
  *  number of rows was swapped and 0 if the matrix is singular. */
-int matrix::division_free_elimination(void)
+int matrix::division_free_elimination(const bool det)
 {
-    int sign = 1;
-    ensure_if_modifiable();
-    for (unsigned r1=0; r1<row-1; ++r1) {
-        int indx = pivot(r1);
-        if (indx==-1)
-            return 0;  // Note: leaves *this in a messy state.
-        if (indx>0)
-            sign = -sign;
-        for (unsigned r2=r1+1; r2<row; ++r2) {
-            for (unsigned c=r1+1; c<col; ++c)
-                this->m[r2*col+c] = this->m[r1*col+r1]*this->m[r2*col+c] - this->m[r2*col+r1]*this->m[r1*col+c];
-            for (unsigned c=0; c<=r1; ++c)
-                this->m[r2*col+c] = _ex0();
-        }
-    }
-    
-    return sign;
+	ensure_if_modifiable();
+	const unsigned m = this->rows();
+	const unsigned n = this->cols();
+	GINAC_ASSERT(!det || n==m);
+	int sign = 1;
+	
+	unsigned r0 = 0;
+	for (unsigned r1=0; (r1<n-1)&&(r0<m-1); ++r1) {
+		int indx = pivot(r0, r1, true);
+		if (indx==-1) {
+			sign = 0;
+			if (det)
+				return 0;  // leaves *this in a messy state
+		}
+		if (indx>=0) {
+			if (indx>0)
+				sign = -sign;
+			for (unsigned r2=r0+1; r2<m; ++r2) {
+				for (unsigned c=r1+1; c<n; ++c)
+					this->m[r2*n+c] = (this->m[r0*n+r1]*this->m[r2*n+c] - this->m[r2*n+r1]*this->m[r0*n+c]).expand();
+				// fill up left hand side with zeros
+				for (unsigned c=0; c<=r1; ++c)
+					this->m[r2*n+c] = _ex0();
+			}
+			if (det) {
+				// save space by deleting no longer needed elements
+				for (unsigned c=r0+1; c<n; ++c)
+					this->m[r0*n+c] = _ex0();
+			}
+			++r0;
+		}
+	}
+	
+	return sign;
 }
 
 
 /** Perform the steps of Bareiss' one-step fraction free elimination to bring
- *  the matrix into an upper echelon form.
- *
+ *  the matrix into an upper echelon form.  Fraction free elimination means
+ *  that divide is used straightforwardly, without computing GCDs first.  This
+ *  is possible, since we know the divisor at each step.
+ *  
+ *  @param det may be set to true to save a lot of space if one is only
+ *  interested in the last element (i.e. for calculating determinants). The
+ *  others are set to zero in this case.
  *  @return sign is 1 if an even number of rows was swapped, -1 if an odd
  *  number of rows was swapped and 0 if the matrix is singular. */
-int matrix::fraction_free_elimination(void)
+int matrix::fraction_free_elimination(const bool det)
 {
-    ensure_if_modifiable();
-    
-    // first normal all elements:
-    for (exvector::iterator i=m.begin(); i!=m.end(); ++i)
-        (*i) = (*i).normal();
-    
-    // FIXME: this is unfinished, once matrix::determinant_bareiss is
-    // bulletproof, some code ought to be copy from there to here.
-    int sign = 1;
-    ex divisor = 1;
-    ex dividend;
-    lst srl;      // symbol replacement list for .to_rational()
-    
-    for (unsigned r1=0; r1<row-1; ++r1) {
-        int indx = pivot(r1);
-        if (indx==-1)
-            return 0;  // Note: leaves *this in a messy state.
-        if (indx>0)
-            sign = -sign;
-        if (r1>0)
-            divisor = this->m[(r1-1)*col+(r1-1)].expand();
-        for (unsigned r2=r1+1; r2<row; ++r2) {
-            for (unsigned c=r1+1; c<col; ++c) {
-                dividend = (this->m[r1*col+r1]*this->m[r2*col+c]
-                           -this->m[r2*col+r1]*this->m[r1*col+c]).expand();
-#ifdef DO_GINAC_ASSERT
-                GINAC_ASSERT(divide(dividend.to_rational(srl),
-                                    divisor.to_rational(srl),
-                                    this->m[r2*col+c]));
-#else
-                divide(dividend.to_rational(srl),
-                       divisor.to_rational(srl),
-                       this->m[r2*col+c]);
-#endif // DO_GINAC_ASSERT
-                this->m[r2*col+c] = this->m[r2*col+c].subs(srl);
-            }
-            for (unsigned c=0; c<=r1; ++c)
-                this->m[r2*col+c] = _ex0();
-        }
-    }
-    
-    return sign;
+	// Method:
+	// (single-step fraction free elimination scheme, already known to Jordan)
+	//
+	// Usual division-free elimination sets m[0](r,c) = m(r,c) and then sets
+	//     m[k+1](r,c) = m[k](k,k) * m[k](r,c) - m[k](r,k) * m[k](k,c).
+	//
+	// Bareiss (fraction-free) elimination in addition divides that element
+	// by m[k-1](k-1,k-1) for k>1, where it can be shown by means of the
+	// Sylvester determinant that this really divides m[k+1](r,c).
+	//
+	// We also allow rational functions where the original prove still holds.
+	// However, we must care for numerator and denominator separately and
+	// "manually" work in the integral domains because of subtle cancellations
+	// (see below).  This blows up the bookkeeping a bit and the formula has
+	// to be modified to expand like this (N{x} stands for numerator of x,
+	// D{x} for denominator of x):
+	//     N{m[k+1](r,c)} = N{m[k](k,k)}*N{m[k](r,c)}*D{m[k](r,k)}*D{m[k](k,c)}
+	//                     -N{m[k](r,k)}*N{m[k](k,c)}*D{m[k](k,k)}*D{m[k](r,c)}
+	//     D{m[k+1](r,c)} = D{m[k](k,k)}*D{m[k](r,c)}*D{m[k](r,k)}*D{m[k](k,c)}
+	// where for k>1 we now divide N{m[k+1](r,c)} by
+	//     N{m[k-1](k-1,k-1)}
+	// and D{m[k+1](r,c)} by
+	//     D{m[k-1](k-1,k-1)}.
+	
+	ensure_if_modifiable();
+	const unsigned m = this->rows();
+	const unsigned n = this->cols();
+	GINAC_ASSERT(!det || n==m);
+	int sign = 1;
+	if (m==1)
+		return 1;
+	ex divisor_n = 1;
+	ex divisor_d = 1;
+	ex dividend_n;
+	ex dividend_d;
+	
+	// We populate temporary matrices to subsequently operate on.  There is
+	// one holding numerators and another holding denominators of entries.
+	// This is a must since the evaluator (or even earlier mul's constructor)
+	// might cancel some trivial element which causes divide() to fail.  The
+	// elements are normalized first (yes, even though this algorithm doesn't
+	// need GCDs) since the elements of *this might be unnormalized, which
+	// makes things more complicated than they need to be.
+	matrix tmp_n(*this);
+	matrix tmp_d(m,n);  // for denominators, if needed
+	lst srl;  // symbol replacement list
+	exvector::iterator it = this->m.begin();
+	exvector::iterator tmp_n_it = tmp_n.m.begin();
+	exvector::iterator tmp_d_it = tmp_d.m.begin();
+	for (; it!= this->m.end(); ++it, ++tmp_n_it, ++tmp_d_it) {
+		(*tmp_n_it) = (*it).normal().to_rational(srl);
+		(*tmp_d_it) = (*tmp_n_it).denom();
+		(*tmp_n_it) = (*tmp_n_it).numer();
+	}
+	
+	unsigned r0 = 0;
+	for (unsigned r1=0; (r1<n-1)&&(r0<m-1); ++r1) {
+		int indx = tmp_n.pivot(r0, r1, true);
+		if (indx==-1) {
+			sign = 0;
+			if (det)
+				return 0;
+		}
+		if (indx>=0) {
+			if (indx>0) {
+				sign = -sign;
+				// tmp_n's rows r0 and indx were swapped, do the same in tmp_d:
+				for (unsigned c=r1; c<n; ++c)
+					tmp_d.m[n*indx+c].swap(tmp_d.m[n*r0+c]);
+			}
+			for (unsigned r2=r0+1; r2<m; ++r2) {
+				for (unsigned c=r1+1; c<n; ++c) {
+					dividend_n = (tmp_n.m[r0*n+r1]*tmp_n.m[r2*n+c]*
+					              tmp_d.m[r2*n+r1]*tmp_d.m[r0*n+c]
+					             -tmp_n.m[r2*n+r1]*tmp_n.m[r0*n+c]*
+					              tmp_d.m[r0*n+r1]*tmp_d.m[r2*n+c]).expand();
+					dividend_d = (tmp_d.m[r2*n+r1]*tmp_d.m[r0*n+c]*
+					              tmp_d.m[r0*n+r1]*tmp_d.m[r2*n+c]).expand();
+					bool check = divide(dividend_n, divisor_n,
+					                    tmp_n.m[r2*n+c], true);
+					check &= divide(dividend_d, divisor_d,
+					                tmp_d.m[r2*n+c], true);
+					GINAC_ASSERT(check);
+				}
+				// fill up left hand side with zeros
+				for (unsigned c=0; c<=r1; ++c)
+					tmp_n.m[r2*n+c] = _ex0();
+			}
+			if ((r1<n-1)&&(r0<m-1)) {
+				// compute next iteration's divisor
+				divisor_n = tmp_n.m[r0*n+r1].expand();
+				divisor_d = tmp_d.m[r0*n+r1].expand();
+				if (det) {
+					// save space by deleting no longer needed elements
+					for (unsigned c=0; c<n; ++c) {
+						tmp_n.m[r0*n+c] = _ex0();
+						tmp_d.m[r0*n+c] = _ex1();
+					}
+				}
+			}
+			++r0;
+		}
+	}
+	// repopulate *this matrix:
+	it = this->m.begin();
+	tmp_n_it = tmp_n.m.begin();
+	tmp_d_it = tmp_d.m.begin();
+	for (; it!= this->m.end(); ++it, ++tmp_n_it, ++tmp_d_it)
+		(*it) = ((*tmp_n_it)/(*tmp_d_it)).subs(srl);
+	
+	return sign;
 }
 
 
-/** Partial pivoting method.
+/** Partial pivoting method for matrix elimination schemes.
  *  Usual pivoting (symbolic==false) returns the index to the element with the
  *  largest absolute value in column ro and swaps the current row with the one
  *  where the element was found.  With (symbolic==true) it does the same thing
  *  with the first non-zero element.
  *
- *  @param ro is the row to be inspected
+ *  @param ro is the row from where to begin
+ *  @param co is the column to be inspected
  *  @param symbolic signal if we want the first non-zero element to be pivoted
  *  (true) or the one with the largest absolute value (false).
  *  @return 0 if no interchange occured, -1 if all are zero (usually signaling
  *  a degeneracy) and positive integer k means that rows ro and k were swapped.
  */
-int matrix::pivot(unsigned ro, bool symbolic)
+int matrix::pivot(unsigned ro, unsigned co, bool symbolic)
 {
-    unsigned k = ro;
-    
-    if (symbolic) {  // search first non-zero
-        for (unsigned r=ro; r<row; ++r) {
-            if (!m[r*col+ro].is_zero()) {
-                k = r;
-                break;
-            }
-        }
-    } else {  // search largest
-        numeric tmp(0);
-        numeric maxn(-1);
-        for (unsigned r=ro; r<row; ++r) {
-            GINAC_ASSERT(is_ex_of_type(m[r*col+ro],numeric));
-            if ((tmp = abs(ex_to_numeric(m[r*col+ro]))) > maxn &&
-                !tmp.is_zero()) {
-                maxn = tmp;
-                k = r;
-            }
-        }
-    }
-    if (m[k*col+ro].is_zero())
-        return -1;
-    if (k!=ro) {  // swap rows
-        ensure_if_modifiable();
-        for (unsigned c=0; c<col; ++c) {
-            m[k*col+c].swap(m[ro*col+c]);
-        }
-        return k;
-    }
-    return 0;
+	unsigned k = ro;
+	if (symbolic) {
+		// search first non-zero element in column co beginning at row ro
+		while ((k<row) && (this->m[k*col+co].expand().is_zero()))
+			++k;
+	} else {
+		// search largest element in column co beginning at row ro
+		GINAC_ASSERT(is_ex_of_type(this->m[k*col+co],numeric));
+		unsigned kmax = k+1;
+		numeric mmax = abs(ex_to_numeric(m[kmax*col+co]));
+		while (kmax<row) {
+			GINAC_ASSERT(is_ex_of_type(this->m[kmax*col+co],numeric));
+			numeric tmp = ex_to_numeric(this->m[kmax*col+co]);
+			if (abs(tmp) > mmax) {
+				mmax = tmp;
+				k = kmax;
+			}
+			++kmax;
+		}
+		if (!mmax.is_zero())
+			k = kmax;
+	}
+	if (k==row)
+		// all elements in column co below row ro vanish
+		return -1;
+	if (k==ro)
+		// matrix needs no pivoting
+		return 0;
+	// matrix needs pivoting, so swap rows k and ro
+	ensure_if_modifiable();
+	for (unsigned c=0; c<col; ++c)
+		this->m[k*col+c].swap(this->m[ro*col+c]);
+	
+	return k;
 }
 
-/** Convert list of lists to matrix. */
-ex lst_to_matrix(const ex &l)
+ex lst_to_matrix(const lst & l)
 {
-	if (!is_ex_of_type(l, lst))
-		throw(std::invalid_argument("argument to lst_to_matrix() must be a lst"));
-
 	// Find number of rows and columns
 	unsigned rows = l.nops(), cols = 0, i, j;
 	for (i=0; i<rows; i++)
@@ -1289,6 +1420,7 @@ ex lst_to_matrix(const ex &l)
 
 	// Allocate and fill matrix
 	matrix &m = *new matrix(rows, cols);
+	m.setflag(status_flags::dynallocated);
 	for (i=0; i<rows; i++)
 		for (j=0; j<cols; j++)
 			if (l.op(i).nops() > j)
@@ -1298,13 +1430,16 @@ ex lst_to_matrix(const ex &l)
 	return m;
 }
 
-//////////
-// global constants
-//////////
+ex diag_matrix(const lst & l)
+{
+	unsigned dim = l.nops();
+
+	matrix &m = *new matrix(dim, dim);
+	m.setflag(status_flags::dynallocated);
+	for (unsigned i=0; i<dim; i++)
+		m.set(i, i, l.op(i));
 
-const matrix some_matrix;
-const type_info & typeid_matrix=typeid(some_matrix);
+	return m;
+}
 
-#ifndef NO_NAMESPACE_GINAC
 } // namespace GiNaC
-#endif // ndef NO_NAMESPACE_GINAC