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Task/Pi/Ruby/pi-1.rb

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+# Calculate Pi using the Arithmetic Geometric Mean of 1 and 1/sqrt(2)
+#
+#
+#  Nigel_Galloway
+#  March 8th., 2012.
+#
+require 'flt'
+Flt::BinNum.Context.precision = 8192
+a = n = 1
+g = 1 / Flt::BinNum(2).sqrt
+z = 0.25
+(0..17).each{
+  x = [(a + g) * 0.5, (a * g).sqrt]
+  var = x[0] - a
+  z -= var * var * n
+  n += n
+  a = x[0]
+  g = x[1]
+}
+puts a * a / z