* Improved lsolve() of systems containing non-numeric coefficients.

[ginac.git] / ginac / matrix.cpp

diff --git a/ginac/matrix.cpp b/ginac/matrix.cpp
index 038084b6486e363ea38b02987fb02268793754dc..821e184d3acc0e8f014e67216f90aba91390778c 100644 (file)
--- a/ginac/matrix.cpp
+++ b/ginac/matrix.cpp
@@ -3,7 +3,7 @@
  *  Implementation of symbolic matrices */
 
 /*
- *  GiNaC Copyright (C) 1999-2007 Johannes Gutenberg University Mainz, Germany
+ *  GiNaC Copyright (C) 1999-2008 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
@@ -222,7 +222,7 @@ ex matrix::eval(int level) const
                        m2[r*col+c] = m[r*col+c].eval(level);
        
        return (new matrix(row, col, m2))->setflag(status_flags::dynallocated |
-                                                                                          status_flags::evaluated);
+                                                  status_flags::evaluated);
 }
 
 ex matrix::subs(const exmap & mp, unsigned options) const
@@ -1414,18 +1414,27 @@ int matrix::fraction_free_elimination(const bool det)
        
        unsigned r0 = 0;
        for (unsigned c0=0; c0<n && r0<m-1; ++c0) {
-               int indx = tmp_n.pivot(r0, c0, true);
-               if (indx==-1) {
+               // When trying to find a pivot, we should try a bit harder than expand().
+               // Searching the first non-zero element in-place here instead of calling
+               // pivot() allows us to do no more substitutions and back-substitutions
+               // than are actually necessary.
+               int indx = r0;
+               while ((indx<m) &&
+                      (tmp_n[indx*n+c0].subs(srl, subs_options::no_pattern).expand().is_zero()))
+                       ++indx;
+               if (indx==m) {
+                       // all elements in column c0 below row r0 vanish
                        sign = 0;
                        if (det)
                                return 0;
-               }
-               if (indx>=0) {
-                       if (indx>0) {
+               } else {
+                       if (indx>r0) {
+                               // Matrix needs pivoting, swap rows r0 and indx of tmp_n and tmp_d.
                                sign = -sign;
-                               // tmp_n's rows r0 and indx were swapped, do the same in tmp_d:
-                               for (unsigned c=c0; c<n; ++c)
+                               for (unsigned c=c0; c<n; ++c) {
+                                       tmp_n.m[n*indx+c].swap(tmp_n.m[n*r0+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=c0+1; c<n; ++c) {