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authorakr <akr@b2dd03c8-39d4-4d8f-98ff-823fe69b080e>2008-02-07 01:43:43 +0000
committerakr <akr@b2dd03c8-39d4-4d8f-98ff-823fe69b080e>2008-02-07 01:43:43 +0000
commit14373fc4db7440d39db4fd39297f2ed44cc990f2 (patch)
tree966d984fadcafb2d9046a161b1e170d99904a592 /math.c
parentb88ecbcffc30fdf8b5743003563e10a347c05b03 (diff)
* math.c (math_gamma): new method Math.gamma.
(math_lgamma): new method Math.lgamma. * include/ruby/missing.h (tgamma): declared unless HAVE_TGAMMA. (lgamma_r): declared unless HAVE_LGAMMA_R. * configure.in (tgamma): check for replacement funtions. (lgamma_r): ditto. * missing/tgamma.c: new file. based on gamma.c from "C-gengo niyoru saishin algorithm jiten" (New Algorithm handbook in C language) (Gijyutsu hyouron sha, Tokyo, 1991) by Haruhiko Okumura. * missing/lgamma_r.c: ditto. * LEGAL (missing/tgamma.c): describe as public domain. (missing/lgamma_r.c): ditto. git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@15388 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
Diffstat (limited to 'math.c')
-rw-r--r--math.c73
1 files changed, 73 insertions, 0 deletions
diff --git a/math.c b/math.c
index 332d899..3a4ed73 100644
--- a/math.c
+++ b/math.c
@@ -487,6 +487,76 @@ math_erfc(VALUE obj, VALUE x)
}
/*
+ * call-seq:
+ * Math.gamma(x) => float
+ *
+ * Calculates the gamma function of x.
+ *
+ * Note that gamma(n) is same as fact(n-1) for integer n >= 0.
+ * However gamma(n) returns float and possibly has error in calculation.
+ *
+ * def fact(n) (1..n).inject(1) {|r,i| r*i } end
+ * 0.upto(25) {|i| p [i, Math.gamma(i+1), fact(i)] }
+ * =>
+ * [0, 1.0, 1]
+ * [1, 1.0, 1]
+ * [2, 2.0, 2]
+ * [3, 6.0, 6]
+ * [4, 24.0, 24]
+ * [5, 120.0, 120]
+ * [6, 720.0, 720]
+ * [7, 5040.0, 5040]
+ * [8, 40320.0, 40320]
+ * [9, 362880.0, 362880]
+ * [10, 3628800.0, 3628800]
+ * [11, 39916800.0, 39916800]
+ * [12, 479001599.999999, 479001600]
+ * [13, 6227020800.00001, 6227020800]
+ * [14, 87178291199.9998, 87178291200]
+ * [15, 1307674368000.0, 1307674368000]
+ * [16, 20922789888000.0, 20922789888000]
+ * [17, 3.55687428096001e+14, 355687428096000]
+ * [18, 6.40237370572799e+15, 6402373705728000]
+ * [19, 1.21645100408832e+17, 121645100408832000]
+ * [20, 2.43290200817664e+18, 2432902008176640000]
+ * [21, 5.10909421717094e+19, 51090942171709440000]
+ * [22, 1.12400072777761e+21, 1124000727777607680000]
+ * [23, 2.58520167388851e+22, 25852016738884976640000]
+ * [24, 6.20448401733239e+23, 620448401733239439360000]
+ * [25, 1.5511210043331e+25, 15511210043330985984000000]
+ *
+ */
+
+static VALUE
+math_gamma(VALUE obj, VALUE x)
+{
+ Need_Float(x);
+ return DOUBLE2NUM(tgamma(RFLOAT_VALUE(x)));
+}
+
+/*
+ * call-seq:
+ * Math.lgamma(x) => [float, -1 or 1]
+ *
+ * Calculates the logarithmic gamma of x and
+ * the sign of gamma of x.
+ *
+ * Math.lgamma(x) is same as
+ * [Math.log(Math.gamma(x)), Math.gamma(x) < 0 ? -1 : 1]
+ * but avoid overflow by Math.gamma(x) for large x.
+ */
+
+static VALUE
+math_lgamma(VALUE obj, VALUE x)
+{
+ int sign;
+ VALUE v;
+ Need_Float(x);
+ v = DOUBLE2NUM(lgamma_r(RFLOAT_VALUE(x), &sign));
+ return rb_assoc_new(v, INT2FIX(sign));
+}
+
+/*
* The <code>Math</code> module contains module functions for basic
* trigonometric and transcendental functions. See class
* <code>Float</code> for a list of constants that
@@ -541,4 +611,7 @@ Init_Math(void)
rb_define_module_function(rb_mMath, "erf", math_erf, 1);
rb_define_module_function(rb_mMath, "erfc", math_erfc, 1);
+
+ rb_define_module_function(rb_mMath, "gamma", math_gamma, 1);
+ rb_define_module_function(rb_mMath, "lgamma", math_lgamma, 1);
}