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MathStuff.cs
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MathStuff.cs
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using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Numerics;
namespace AdvancedConsoleApplicationV
{
/// <summary>
/// Adapted from: http://kashfarooq.wordpress.com/2011/07/23/calculating-pi-in-c-part-2-using-the-net-4-biginteger-class/
/// </summary>
class MathStuff
{
public static BigInteger InverseTan(int denominator, int numberOfDigitsRequired)
{
int demonimatorSquared = denominator * denominator;
int degreeNeeded = GetDegreeOfPrecisionNeeded(demonimatorSquared, numberOfDigitsRequired);
BigInteger tenToNumberPowerOfDigitsRequired = GetTenToPowerOfNumberOfDigitsRequired(numberOfDigitsRequired);
int c = 2 * degreeNeeded + 1;
BigInteger s = BigInteger.Divide(tenToNumberPowerOfDigitsRequired, new BigInteger(c));
for (int i = 0; i < degreeNeeded; i++)
{
c -= 2;
BigInteger temp1 = BigInteger.Divide(tenToNumberPowerOfDigitsRequired, new BigInteger(c));
BigInteger temp2 = BigInteger.Divide(s, new BigInteger(demonimatorSquared));
s = BigInteger.Subtract(temp1, temp2);
}
return BigInteger.Divide(s, new BigInteger(denominator));
}
private static int GetDegreeOfPrecisionNeeded(int demonimatorSquared, int numberOfDigitsRequired)
{
int degreeNeeded = 0;
while ((Math.Log(2 * degreeNeeded + 3) + (degreeNeeded + 1) * Math.Log10(demonimatorSquared)) <= numberOfDigitsRequired * Math.Log(10))
{
degreeNeeded++;
}
return degreeNeeded;
}
private static BigInteger GetTenToPowerOfNumberOfDigitsRequired(int numberOfDigitsRequired)
{
BigInteger tenToNumberOfDigitsRequired = new BigInteger(10);
BigInteger pow = BigInteger.Pow(tenToNumberOfDigitsRequired, numberOfDigitsRequired);
return pow;
}
public static string Calculate(int numberOfDigitsRequired)
{
numberOfDigitsRequired += 8; // To be safe, compute 8 extra digits, to be dropped at end. The 8 is arbitrary
BigInteger a = BigInteger.Multiply(InverseTan(5, numberOfDigitsRequired), new BigInteger(16)); //16 x arctan(1/5)
BigInteger b = BigInteger.Multiply(InverseTan(239, numberOfDigitsRequired), new BigInteger(4)); //4 x arctan(1/239)
BigInteger pi = BigInteger.Subtract(a, b);
string piAsString = BigInteger.Divide(pi, new BigInteger(100000000)).ToString();
string piFormatted = piAsString[0] + "." + piAsString.Substring(1, numberOfDigitsRequired - 8);
return piFormatted;
}
}
}