From: Christian Bauer Date: Thu, 21 Nov 2002 22:57:06 +0000 (+0000) Subject: added collect_common_factors() (is this a good name?) X-Git-Tag: release_1-0-13~14 X-Git-Url: https://www.ginac.de/ginac.git//ginac.git?p=ginac.git;a=commitdiff_plain;h=3dfe5d31528291d1be6b1fe1180622efdabfebde;hp=778927a23b7807cb9809047211265000650eda56 added collect_common_factors() (is this a good name?) --- diff --git a/ginac/normal.cpp b/ginac/normal.cpp index 5e6aa470..67091f50 100644 --- a/ginac/normal.cpp +++ b/ginac/normal.cpp @@ -1912,6 +1912,96 @@ ex sqrfree_parfrac(const ex & a, const symbol & x) } +/** Remove the common factor in the terms of a sum 'e' by calculating the GCD, + * and multiply it into the expression 'factor' (which needs to be initialized + * to 1, unless you're accumulating factors). */ +static ex find_common_factor(const ex & e, ex & factor) +{ + if (is_a(e)) { + + unsigned num = e.nops(); + exvector terms; terms.reserve(num); + lst repl; + ex gc; + + // Find the common GCD + for (unsigned i=0; i(x) || is_a(x)) { + ex f = 1; + x = find_common_factor(x, f); + x *= f; + } + + if (i == 0) + gc = x; + else + gc = gcd(gc, x); + + terms.push_back(x); + } + + if (gc.is_equal(_ex1)) + return e; + + // The GCD is the factor we pull out + factor *= gc.subs(repl); + + // Now divide all terms by the GCD + for (unsigned i=0; i(t)) { + for (unsigned j=0; jsetflag(status_flags::dynallocated).subs(repl); + goto term_done; + } + } + } + + divide(t, gc, x); + t = x.subs(repl); +term_done: ; + } + return (new add(terms))->setflag(status_flags::dynallocated); + + } else if (is_a(e)) { + + exvector v; + for (unsigned i=0; isetflag(status_flags::dynallocated); + + } else + return e; +} + + +/** Collect common factors in sums. This converts expressions like + * 'a*(b*x+b*y)' to 'a*b*(x+y)'. */ +ex collect_common_factors(const ex & e) +{ + if (is_a(e) || is_a(e)) { + + ex factor = 1; + ex r = find_common_factor(e, factor); + return factor * r; + + } else + return e; +} + + /* * Normal form of rational functions */ diff --git a/ginac/normal.h b/ginac/normal.h index be67d8eb..9196f965 100644 --- a/ginac/normal.h +++ b/ginac/normal.h @@ -63,6 +63,9 @@ extern ex sqrfree(const ex &a, const lst &l = lst()); // Square-free partial fraction decomposition of a rational function a(x) extern ex sqrfree_parfrac(const ex & a, const symbol & x); +// Collect common factors in sums. +extern ex collect_common_factors(const ex & e); + } // namespace GiNaC #endif // ndef __GINAC_NORMAL_H__