From: Christian Bauer <Christian.Bauer@uni-mainz.de>
Date: Wed, 6 Oct 2004 15:38:02 +0000 (+0000)
Subject: synced to HEAD (binomial())
X-Git-Tag: release_1-2-4~5
X-Git-Url: https://www.ginac.de/ginac.git/static/git-favicon.png/ginac.git?a=commitdiff_plain;h=0c0833bb36921d6546ce87c6bef959330b561a9e;p=ginac.git

synced to HEAD (binomial())
---

diff --git a/NEWS b/NEWS
index a188df7f..37b6c5fc 100644
--- a/NEWS
+++ b/NEWS
@@ -1,5 +1,8 @@
 This file records noteworthy changes.
 
+1.2.4 (<date>)
+* binomial(n, k) evaluates for non-integer arguments n.
+
 1.2.3 (13 August 2004)
 * Added variants of dirac_trace() and color_trace() that take the trace over
   more than one representation label by specifying a set or list of labels.
diff --git a/ginac/inifcns.cpp b/ginac/inifcns.cpp
index fa5e9a20..decef1a8 100644
--- a/ginac/inifcns.cpp
+++ b/ginac/inifcns.cpp
@@ -485,11 +485,32 @@ static ex binomial_evalf(const ex & x, const ex & y)
 	return binomial(x, y).hold();
 }
 
+static ex binomial_sym(const ex & x, const numeric & y)
+{
+	if (y.is_integer()) {
+		if (y.is_nonneg_integer()) {
+			const unsigned N = y.to_int();
+			if (N == 0) return _num0;
+			if (N == 1) return x;
+			ex t = x.expand();
+			for (unsigned i = 2; i <= N; ++i)
+				t = (t * (x + i - y - 1)).expand() / i;
+			return t;
+		} else
+			return _num0;
+	}
+
+	return binomial(x, y).hold();
+}
+
 static ex binomial_eval(const ex & x, const ex &y)
 {
-	if (is_exactly_a<numeric>(x) && is_exactly_a<numeric>(y))
-		return binomial(ex_to<numeric>(x), ex_to<numeric>(y));
-	else
+	if (is_exactly_a<numeric>(y)) {
+		if (is_exactly_a<numeric>(x) && ex_to<numeric>(x).is_integer())
+			return binomial(ex_to<numeric>(x), ex_to<numeric>(y));
+		else
+			return binomial_sym(x, ex_to<numeric>(y));
+	} else
 		return binomial(x, y).hold();
 }
 
diff --git a/ginac/numeric.cpp b/ginac/numeric.cpp
index b6c95e01..3130e272 100644
--- a/ginac/numeric.cpp
+++ b/ginac/numeric.cpp
@@ -1629,7 +1629,7 @@ const numeric binomial(const numeric &n, const numeric &k)
 	}
 	
 	// should really be gamma(n+1)/gamma(k+1)/gamma(n-k+1) or a suitable limit
-	throw std::range_error("numeric::binomial(): don´t know how to evaluate that.");
+	throw std::range_error("numeric::binomial(): don't know how to evaluate that.");
 }