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Task/Gamma-function/FreeBASIC/gamma-function.freebasic

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+' FB 1.05.0 Win64
+
+Const pi = 3.1415926535897932
+Const e  = 2.7182818284590452
+
+Function gammaStirling (x As Double) As Double
+  Return Sqr(2.0 * pi / x) * ((x / e) ^ x)
+End Function
+
+Function gammaLanczos (x As Double) As Double
+  Dim p(0 To 8) As Double = _
+  { _
+       0.99999999999980993, _
+     676.5203681218851, _
+   -1259.1392167224028, _			     	
+     771.32342877765313, _
+    -176.61502916214059, _
+      12.507343278686905, _
+      -0.13857109526572012, _
+       9.9843695780195716e-6, _
+       1.5056327351493116e-7 _
+  }
+
+  Dim As Integer g = 7
+  If x < 0.5 Then Return pi / (Sin(pi * x) * gammaLanczos(1-x))
+  x -= 1
+  Dim a As Double = p(0)
+  Dim t As Double = x + g + 0.5
+
+  For i As Integer = 1 To 7
+    a += p(i) / (x + i)
+  Next		
+
+  Return Sqr(2.0 * pi) * (t ^ (x + 0.5)) * Exp(-t) * a
+End Function
+
+Print " x", "    Stirling",, "    Lanczos"
+Print
+For i As Integer = 1 To 20
+   Dim As Double d = i / 10.0
+   Print   Using "#.##"; d;
+   Print , Using "#.###############"; gammaStirling(d);
+   Print , Using "#.###############"; gammaLanczos(d)
+Next
+Print
+Print "Press any key to quit"
+Sleep