Additional transformations for mul and power [Sheplyakov].

[ginac.git] / ginac / power.cpp

diff --git a/ginac/power.cpp b/ginac/power.cpp
index 5d2ec7046d895bf56ea62fbd64beb7b63ef32f19..8829bbae597788f6908e2c4739d68da24ea42619 100644 (file)
--- a/ginac/power.cpp
+++ b/ginac/power.cpp
@@ -3,7 +3,7 @@
  *  Implementation of GiNaC's symbolic exponentiation (basis^exponent). */
 
 /*
- *  GiNaC Copyright (C) 1999-2006 Johannes Gutenberg University Mainz, Germany
+ *  GiNaC Copyright (C) 1999-2007 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
@@ -467,8 +467,9 @@ ex power::eval(int level) const
                        if (is_exactly_a<numeric>(sub_exponent)) {
                                const numeric & num_sub_exponent = ex_to<numeric>(sub_exponent);
                                GINAC_ASSERT(num_sub_exponent!=numeric(1));
-                               if (num_exponent->is_integer() || (abs(num_sub_exponent) - (*_num1_p)).is_negative())
+                               if (num_exponent->is_integer() || (abs(num_sub_exponent) - (*_num1_p)).is_negative()) {
                                        return power(sub_basis,num_sub_exponent.mul(*num_exponent));
+                               }
                        }
                }
        
@@ -476,7 +477,31 @@ ex power::eval(int level) const
                if (num_exponent->is_integer() && is_exactly_a<mul>(ebasis)) {
                        return expand_mul(ex_to<mul>(ebasis), *num_exponent, 0);
                }
-       
+
+               // (2*x + 6*y)^(-4) -> 1/16*(x + 3*y)^(-4)
+               if (num_exponent->is_integer() && is_exactly_a<add>(ebasis)) {
+                       const numeric icont = ebasis.integer_content();
+                       const numeric& lead_coeff = 
+                               ex_to<numeric>(ex_to<add>(ebasis).seq.begin()->coeff).div_dyn(icont);
+
+                       const bool canonicalizable = lead_coeff.is_integer();
+                       const bool unit_normal = lead_coeff.is_pos_integer();
+
+                       if (icont != *_num1_p) {
+                               return (new mul(power(ebasis/icont, *num_exponent), power(icont, *num_exponent))
+                                      )->setflag(status_flags::dynallocated);
+                       }
+
+                       if (canonicalizable && (! unit_normal)) {
+                               if (num_exponent->is_even()) {
+                                       return power(-ebasis, *num_exponent);
+                               } else {
+                                       return (new mul(power(-ebasis, *num_exponent), *_num_1_p)
+                                              )->setflag(status_flags::dynallocated);
+                               }
+                       }
+               }
+
                // ^(*(...,x;c1),c2) -> *(^(*(...,x;1),c2),c1^c2)  (c1, c2 numeric(), c1>0)
                // ^(*(...,x;c1),c2) -> *(^(*(...,x;-1),c2),(-c1)^c2)  (c1, c2 numeric(), c1<0)
                if (is_exactly_a<mul>(ebasis)) {
@@ -943,7 +968,7 @@ ex power::expand_add_2(const add & a, unsigned options) const
        return (new add(sum))->setflag(status_flags::dynallocated | status_flags::expanded);
 }
 
-/** Expand factors of m in m^n where m is a mul and n is and integer.
+/** Expand factors of m in m^n where m is a mul and n is an integer.
  *  @see power::expand */
 ex power::expand_mul(const mul & m, const numeric & n, unsigned options, bool from_expand) const
 {