From: Jens Vollinga <vollinga@thep.physik.uni-mainz.de>
Date: Tue, 12 Dec 2006 17:22:24 +0000 (+0000)
Subject: Bug in numerical evaluation of multiple polylogs fixed.
X-Git-Tag: release_1-4-0~44
X-Git-Url: https://www.ginac.de/ginac.git//ginac.git?p=ginac.git;a=commitdiff_plain;h=8bf3668614986630b9a2825d4fde73a0c1f2c31c;hp=d9eaa10644d2f0d000b8cbae47d8544fcf646f91

Bug in numerical evaluation of multiple polylogs fixed.
---

diff --git a/ginac/inifcns_nstdsums.cpp b/ginac/inifcns_nstdsums.cpp
index 1fd80aef..5215dd8d 100644
--- a/ginac/inifcns_nstdsums.cpp
+++ b/ginac/inifcns_nstdsums.cpp
@@ -471,7 +471,13 @@ namespace {
 // performs the actual series summation for multiple polylogarithms
 cln::cl_N multipleLi_do_sum(const std::vector<int>& s, const std::vector<cln::cl_N>& x)
 {
+	// ensure all x <> 0.
+	for (std::vector<cln::cl_N>::const_iterator it = x.begin(); it != x.end(); ++it) {
+		if ( *it == 0 ) return cln::cl_float(0, cln::float_format(Digits));
+	}
+
 	const int j = s.size();
+	bool flag_accidental_zero = false;
 
 	std::vector<cln::cl_N> t(j);
 	cln::cl_F one = cln::cl_float(1, cln::float_format(Digits));
@@ -480,19 +486,13 @@ cln::cl_N multipleLi_do_sum(const std::vector<int>& s, const std::vector<cln::cl
 	int q = 0;
 	do {
 		t0buf = t[0];
-		// do it once ...
-		q++;
-		t[j-1] = t[j-1] + cln::expt(x[j-1], q) / cln::expt(cln::cl_I(q),s[j-1]) * one;
-		for (int k=j-2; k>=0; k--) {
-			t[k] = t[k] + t[k+1] * cln::expt(x[k], q+j-1-k) / cln::expt(cln::cl_I(q+j-1-k), s[k]);
-		}
-		// ... and do it again (to avoid premature drop out due to special arguments)
 		q++;
 		t[j-1] = t[j-1] + cln::expt(x[j-1], q) / cln::expt(cln::cl_I(q),s[j-1]) * one;
 		for (int k=j-2; k>=0; k--) {
+			flag_accidental_zero = cln::zerop(t[k+1]);
 			t[k] = t[k] + t[k+1] * cln::expt(x[k], q+j-1-k) / cln::expt(cln::cl_I(q+j-1-k), s[k]);
 		}
-	} while (t[0] != t0buf);
+	} while ( (t[0] != t0buf) || flag_accidental_zero );
 
 	return t[0];
 }