Data commit

Task/Gamma-function/Jsish/gamma-function.jsish

@@ -0,0 +1,56 @@
+#!/usr/bin/env jsish
+/* Gamma function, in Jsish, using the Lanczos approximation */
+function gamma(x) {
+    var p = [0.99999999999980993, 676.5203681218851, -1259.1392167224028,
+        771.32342877765313, -176.61502916214059, 12.507343278686905,
+        -0.13857109526572012, 9.9843695780195716e-6, 1.5056327351493116e-7
+    ];
+
+    var g = 7;
+    if (x < 0.5) {
+        return Math.PI / (Math.sin(Math.PI * x) * gamma(1 - x));
+    }
+
+    x -= 1;
+    var a = p[0];
+    var t = x + g + 0.5;
+    for (var i = 1; i < p.length; i++) {
+        a += p[i] / (x + i);
+    }
+
+    return Math.sqrt(2 * Math.PI) * Math.pow(t, x + 0.5) * Math.exp(-t) * a;
+}
+
+if (Interp.conf('unitTest')) {
+    for (var i=-5.5; i <= 5.5; i += 0.5) {
+        printf('%2.1f %+e\n', i, gamma(i));
+    }
+}
+
+/*
+=!EXPECTSTART!=
+-5.5 +1.091265e-02
+-5.0 -4.275508e+13
+-4.5 -6.001960e-02
+-4.0 +2.672193e+14
+-3.5 +2.700882e-01
+-3.0 -1.425169e+15
+-2.5 -9.453087e-01
+-2.0 +6.413263e+15
+-1.5 +2.363272e+00
+-1.0 -2.565305e+16
+-0.5 -3.544908e+00
+0.0 +inf
+0.5 +1.772454e+00
+1.0 +1.000000e+00
+1.5 +8.862269e-01
+2.0 +1.000000e+00
+2.5 +1.329340e+00
+3.0 +2.000000e+00
+3.5 +3.323351e+00
+4.0 +6.000000e+00
+4.5 +1.163173e+01
+5.0 +2.400000e+01
+5.5 +5.234278e+01
+=!EXPECTEND!=
+*/