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A simple PI calculator in C#.
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Numerics;
namespace PiCalculator
{
public class PiCalculator
{
// Pi = 16 * arctan(1/5) - 4 * arctan(1/239)
public BigInteger GetPi(int digits, int iterations)
{
return 16 * BigMath.ArcTan1OverX(5, digits).ElementAt(iterations)
- 4 * BigMath.ArcTan1OverX(239, digits).ElementAt(iterations);
}
}
public static class BigMath
{
//arctan(x) = x - x^3/3 + x^5/5 - x^7/7 + x^9/9 - ...
public static IEnumerable<BigInteger> ArcTan1OverX(int x, int digits)
{
var mag = BigInteger.Pow(10, digits);
var sum = BigInteger.Zero;
bool sign = true;
for (int i = 1; true; i += 2)
{
var cur = mag / (BigInteger.Pow(x, i) * i);
if (sign)
{
sum += cur;
}
else
{
sum -= cur;
}
yield return sum;
sign = !sign;
}
}
}
}
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