* Implementation of GiNaC's special tensors. */
/*
- * GiNaC Copyright (C) 1999-2001 Johannes Gutenberg University Mainz, Germany
+ * GiNaC Copyright (C) 1999-2003 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
const idx & i1 = ex_to<idx>(i.op(1));
const idx & i2 = ex_to<idx>(i.op(2));
- // Trace of delta tensor is the dimension of the space
- if (is_dummy_pair(i1, i2))
- return i1.get_dim();
+ // The dimension of the indices must be equal, otherwise we use the minimal
+ // dimension
+ if (!i1.get_dim().is_equal(i2.get_dim())) {
+ ex min_dim = i1.minimal_dim(i2);
+ return i.subs(lst(i1 == i1.replace_dim(min_dim), i2 == i2.replace_dim(min_dim)));
+ }
+
+ // Trace of delta tensor is the (effective) dimension of the space
+ if (is_dummy_pair(i1, i2)) {
+ try {
+ return i1.minimal_dim(i2);
+ } catch (std::exception &e) {
+ return i.hold();
+ }
+ }
// Numeric evaluation
if (static_cast<const indexed &>(i).all_index_values_are(info_flags::integer)) {
const varidx & i1 = ex_to<varidx>(i.op(1));
const varidx & i2 = ex_to<varidx>(i.op(2));
+ // The dimension of the indices must be equal, otherwise we use the minimal
+ // dimension
+ if (!i1.get_dim().is_equal(i2.get_dim())) {
+ ex min_dim = i1.minimal_dim(i2);
+ return i.subs(lst(i1 == i1.replace_dim(min_dim), i2 == i2.replace_dim(min_dim)));
+ }
+
// A metric tensor with one covariant and one contravariant index gets
// replaced by a delta tensor
if (i1.is_covariant() != i2.is_covariant())
return i.hold();
}
-/** Contraction of an indexed delta tensor with something else. */
-bool tensdelta::contract_with(exvector::iterator self, exvector::iterator other, exvector & v) const
+bool tensor::replace_contr_index(exvector::iterator self, exvector::iterator other) const
{
- GINAC_ASSERT(is_a<indexed>(*self));
- GINAC_ASSERT(is_a<indexed>(*other));
- GINAC_ASSERT(self->nops() == 3);
- GINAC_ASSERT(is_a<tensdelta>(self->op(0)));
-
- // Try to contract first index
+ // Try to contract the first index
const idx *self_idx = &ex_to<idx>(self->op(1));
const idx *free_idx = &ex_to<idx>(self->op(2));
bool first_index_tried = false;
const idx &other_idx = ex_to<idx>(other->op(i));
if (is_dummy_pair(*self_idx, other_idx)) {
- // Contraction found, remove delta tensor and substitute
- // index in second object
- *self = _ex1;
- *other = other->subs(other_idx == *free_idx);
- return true;
+ // Contraction found, remove this tensor and substitute the
+ // index in the second object
+ try {
+ // minimal_dim() throws an exception when index dimensions are not comparable
+ ex min_dim = self_idx->minimal_dim(other_idx);
+ *other = other->subs(other_idx == free_idx->replace_dim(min_dim));
+ *self = _ex1; // *other is assigned first because assigning *self invalidates free_idx
+ return true;
+ } catch (std::exception &e) {
+ return false;
+ }
}
}
}
if (!first_index_tried) {
- // No contraction with first index found, try second index
+ // No contraction with the first index found, try the second index
self_idx = &ex_to<idx>(self->op(2));
free_idx = &ex_to<idx>(self->op(1));
first_index_tried = true;
return false;
}
+/** Contraction of an indexed delta tensor with something else. */
+bool tensdelta::contract_with(exvector::iterator self, exvector::iterator other, exvector & v) const
+{
+ GINAC_ASSERT(is_a<indexed>(*self));
+ GINAC_ASSERT(is_a<indexed>(*other));
+ GINAC_ASSERT(self->nops() == 3);
+ GINAC_ASSERT(is_a<tensdelta>(self->op(0)));
+
+ // Replace the dummy index with this tensor's other index and remove
+ // the tensor (this is valid for contractions with all other tensors)
+ return replace_contr_index(self, other);
+}
+
/** Contraction of an indexed metric tensor with something else. */
bool tensmetric::contract_with(exvector::iterator self, exvector::iterator other, exvector & v) const
{
if (is_ex_of_type(other->op(0), tensdelta))
return false;
- // Try to contract first index
- const idx *self_idx = &ex_to<idx>(self->op(1));
- const idx *free_idx = &ex_to<idx>(self->op(2));
- bool first_index_tried = false;
-
-again:
- if (self_idx->is_symbolic()) {
- for (unsigned i=1; i<other->nops(); i++) {
- const idx &other_idx = ex_to<idx>(other->op(i));
- if (is_dummy_pair(*self_idx, other_idx)) {
-
- // Contraction found, remove metric tensor and substitute
- // index in second object
- *self = _ex1;
- *other = other->subs(other_idx == *free_idx);
- return true;
- }
- }
- }
-
- if (!first_index_tried) {
-
- // No contraction with first index found, try second index
- self_idx = &ex_to<idx>(self->op(2));
- free_idx = &ex_to<idx>(self->op(1));
- first_index_tried = true;
- goto again;
- }
-
- return false;
+ // Replace the dummy index with this tensor's other index and remove
+ // the tensor (this is valid for contractions with all other tensors)
+ return replace_contr_index(self, other);
}
/** Contraction of an indexed spinor metric with something else. */
if (is_dummy_pair(*self_idx, other_idx)) {
// Contraction found, remove metric tensor and substitute
- // index in second object
- *self = (static_cast<const spinidx *>(self_idx)->is_covariant() ? sign : -sign);
+ // index in second object (assign *self last because this
+ // invalidates free_idx)
*other = other->subs(other_idx == *free_idx);
+ *self = (static_cast<const spinidx *>(self_idx)->is_covariant() ? sign : -sign);
return true;
}
}
if (is_ex_exactly_of_type(other->op(0), tensepsilon) && num+1 == other->nops()) {
// Contraction of two epsilon tensors is a determinant
- ex dim = ex_to<idx>(self->op(1)).get_dim();
+ bool variance = is_a<varidx>(self->op(1));
matrix M(num, num);
for (int i=0; i<num; i++) {
for (int j=0; j<num; j++) {
if (minkowski)
M(i, j) = lorentz_g(self->op(i+1), other->op(j+1), pos_sig);
- else
+ else if (variance)
M(i, j) = metric_tensor(self->op(i+1), other->op(j+1));
+ else
+ M(i, j) = delta_tensor(self->op(i+1), other->op(j+1));
}
}
int sign = minkowski ? -1 : 1;
*self = sign * M.determinant().simplify_indexed();
*other = _ex1;
return true;
-
- } else if (other->return_type() == return_types::commutative) {
-
-#if 0
- // This handles eps.i.j.k * p.j * p.k = 0
- // Maybe something like this should go to simplify_indexed() because
- // such relations are true for any antisymmetric tensors...
- exvector c;
-
- // Handle all indices of the epsilon tensor
- for (int i=0; i<num; i++) {
- ex idx = self->op(i+1);
-
- // Look whether there's a contraction with this index
- exvector::const_iterator ait, aitend = v.end();
- for (ait = v.begin(); ait != aitend; ait++) {
- if (ait == self)
- continue;
- if (is_a<indexed>(*ait) && ait->return_type() == return_types::commutative && ex_to<indexed>(*ait).has_dummy_index_for(idx) && ait->nops() == 2) {
-
- // Yes, did we already have another contraction with the same base expression?
- ex base = ait->op(0);
- if (std::find_if(c.begin(), c.end(), bind2nd(ex_is_equal(), base)) == c.end()) {
-
- // No, add the base expression to the list
- c.push_back(base);
-
- } else {
-
- // Yes, the contraction is zero
- *self = _ex0;
- *other = _ex0;
- return true;
- }
- }
- }
- }
-#endif
}
return false;
return indexed(tensepsilon(true, pos_sig), sy_anti(), i1, i2, i3, i4);
}
-ex eps0123(const ex & i1, const ex & i2, const ex & i3, const ex & i4, bool pos_sig)
-{
- if (!is_ex_of_type(i1, varidx) || !is_ex_of_type(i2, varidx) || !is_ex_of_type(i3, varidx) || !is_ex_of_type(i4, varidx))
- throw(std::invalid_argument("indices of epsilon tensor must be of type varidx"));
-
- ex dim = ex_to<idx>(i1).get_dim();
- if (dim.is_equal(4))
- return lorentz_eps(i1, i2, i3, i4, pos_sig);
- else
- return indexed(tensepsilon(true, pos_sig), sy_anti(), i1, i2, i3, i4);
-}
-
} // namespace GiNaC
git://www.ginac.de / ginac.git / blobdiff