Gauss.cs

using System;
class Gauss
{
	static double[,] matrix = {{1.334E-4, 4.123E+1, 7.912E+2, -1.544E+3, -711.5698662},
	{1.777, 2.367E-5, 2.07E+1, -9.035E+1, -67.87297633},
	{9.188, 0, -1.015E+1, 1.988E-4, -0.9618012},
	{1.002E+2, 1.442E+4, -7.014E+2, 5.321, 13824.121}};
	static double[,] matrix2 = {{1.334E-4, 4.123E+1, 7.912E+2, -1.544E+3, -711.5698662},
	{1.777, 2.367E-5, 2.07E+1, -9.035E+1, -67.87297633},
	{9.188, 0, -1.015E+1, 1.988E-4, -0.9618012},
	{1.002E+2, 1.442E+4, -7.014E+2, 5.321, 13824.121}};
	static int n = 4;
	public static void Main()
	{
		double[] ans = new double[n];
		Console.WriteLine("With out pivot:");
		GaussElim();
		Cal(ans);
		PrintAnsElim(ans);

		Console.WriteLine("With pivot:");
		matrix = matrix2;
		Pivot();
		GaussElim();
		Cal(ans);
		PrintAnsElim(ans);
	}
	static void PrintAnsElim(double[] ans)
	{
		for(int i=0 ; i<n ; i++)
			Console.WriteLine("{0}",ans[i]);
	}
	static void Print()
	{
		for(int i=0 ;i<n ; i++)
		{
			for(int j=0 ; j<n+1 ; j++)
			{
				Console.Write("{0} ",matrix[i,j]);
			}
			Console.WriteLine();
		}
	}
	static void Pivot()
	{
		for(int i=0 ; i<n ; i++){
			for(int j=0 ; j<n ; j++){
				if(matrix[i,0]>matrix[j,0]){
					for(int k=0 ; k<n+1 ; k++){
						Swap(ref matrix[i,k],ref matrix[j,k]);
					}
				}
			}
		}
	}
	static void Swap(ref double a,ref double b)
	{
		double tmp = a;
		a = b;
		b = tmp;
	}
	static void GaussElim()
	{
		int i,j,k;
		double a,b;
		for(j=0 ; j<n-1 ; j++)
		{
			for(i=j+1 ; i<n ; i++)
			{
				a = matrix[i,j];
				b = matrix[j,j];
				for(k=j ; k<n+1 ; k++)
				{
					matrix[i,k] -=matrix[j,k]*a/b;
				}
			}
		}
	}
	static void Cal(double[] ans)
	{
		int i,j;
		for(i = n-1 ; i>=0 ; i--)
		{
			for(j = n-1 ; j>=i ; j--)
			{
				if(j == i)
				{
					ans[i] = matrix[i,n]/matrix[i,j];
				}
				else
				{
					matrix[i,n] -= matrix[i,j]*ans[j];
				}
			}
		}
	}
}