Make power::expand() (x*p)^c -> x^c * p^c, if p>0.

[ginac.git] / ginac / power.cpp

diff --git a/ginac/power.cpp b/ginac/power.cpp
index 6d6f81daa0992073e1c5818fae906ceb5a6b9372..82200d7abd3f6355a01a9a30dea074dc370aea7e 100644 (file)
--- a/ginac/power.cpp
+++ b/ginac/power.cpp
@@ -799,6 +799,51 @@ ex power::expand(unsigned options) const
                return *this;
        }
 
+       // (x*p)^c -> x^c * p^c, if p>0
+       // makes sense before expanding the basis
+       if (is_exactly_a<mul>(basis) && !basis.info(info_flags::indefinite)) {
+               const mul &m = ex_to<mul>(basis);
+               exvector prodseq;
+               epvector powseq;
+               prodseq.reserve(m.seq.size() + 1);
+               powseq.reserve(m.seq.size() + 1);
+               epvector::const_iterator last = m.seq.end();
+               epvector::const_iterator cit = m.seq.begin();
+               bool possign = true;
+
+               // search for positive/negative factors
+               while (cit!=last) {
+                       ex e=m.recombine_pair_to_ex(*cit);
+                       if (e.info(info_flags::positive))
+                               prodseq.push_back(pow(e, exponent).expand(options));
+                       else if (e.info(info_flags::negative)) {
+                               prodseq.push_back(pow(-e, exponent).expand(options));
+                               possign = !possign;
+                       } else
+                               powseq.push_back(*cit);
+                       ++cit;
+               }
+
+               // take care on the numeric coefficient
+               ex coeff=(possign? _ex1 : _ex_1);
+               if (m.overall_coeff.info(info_flags::positive) && m.overall_coeff != _ex1)
+                       prodseq.push_back(power(m.overall_coeff, exponent));
+               else if (m.overall_coeff.info(info_flags::negative) && m.overall_coeff != _ex_1)
+                       prodseq.push_back(power(-m.overall_coeff, exponent));
+               else
+                       coeff *= m.overall_coeff;
+
+               // If positive/negative factors are found, then extract them.
+               // In either case we set a flag to avoid the second run on a part
+               // which does not have positive/negative terms.
+               if (prodseq.size() > 0) {
+                       ex newbasis = coeff*mul(powseq);
+                       ex_to<basic>(newbasis).setflag(status_flags::purely_indefinite);
+                       return ((new mul(prodseq))->setflag(status_flags::dynallocated)*(new power(newbasis, exponent))->setflag(status_flags::dynallocated).expand(options)).expand(options);
+               } else
+                       ex_to<basic>(basis).setflag(status_flags::purely_indefinite);
+       }
+
        const ex expanded_basis = basis.expand(options);
        const ex expanded_exponent = exponent.expand(options);