TheAlgorithms-C/numerical_methods/Gauss_Elimination.c

#include <stdio.h>
#include <math.h>

#define ARRAY_SIZE 20

void display(float a[ARRAY_SIZE][ARRAY_SIZE], int n)
{
	int i, j;
	for (i = 0; i < n; i++)
	{
		for (j = 0; j <= n; j++)
		{
			printf("%.2f \t", a[i][j]);
		}
		printf("\n");
	}
}

float interchange(float m[ARRAY_SIZE][ARRAY_SIZE], int i, int n)
{
	float tmp[ARRAY_SIZE][ARRAY_SIZE];
	float max = fabs(m[i][i]);
	int j, k = i;

	for (j = i; j < n; j++)
	{
		if (max < fabs(m[j][i]))
		{
			max = fabs(m[j][i]);
			k = j;
		}
	}
	for (j = 0; j <= n; j++)
	{
		tmp[i][j] = m[i][j];
		m[i][j] = m[k][j];
		m[k][j] = tmp[i][j];
	}
	return m[ARRAY_SIZE - 1][ARRAY_SIZE - 1];
}
float eliminate(float m[ARRAY_SIZE][ARRAY_SIZE], int i, int n)
{
	float tmp;
	int k = 1, l, j;
	for (j = i; j < n - 1; j++)
	{
		tmp = -((m[i + k][i]) / (m[i][i]));
		for (l = 0; l <= n; l++)
		{
			m[i + k][l] = (m[i + k][l]) + (m[i][l] * tmp);
		}
		k++;
	}
	return m[ARRAY_SIZE - 1][ARRAY_SIZE - 1];
}
int main(void)
{
	int i, j, n, k = 0, l;
	float m[ARRAY_SIZE][ARRAY_SIZE], mul, tmp[ARRAY_SIZE][ARRAY_SIZE], val, ans[ARRAY_SIZE];

	printf("Total No.of Equations : ");
	scanf("%d", &n);

	printf("\n");
	for (i = 0; i < n; i++)
	{

		printf("Enter Co-efficient Of Equations %d & Total --->>>\n", i + 1);
		for (j = 0; j <= n; j++)
		{
			printf("r%d%d : ", i, j);
			scanf("%f", &m[i][j]);
		}
		printf("\n");
	}
	printf(":::::::::::: Current Matrix ::::::::::::\n\n");
	display(m, n);

	for (i = 0; i < n - 1; i++)
	{
		printf("\n------->>>>>>>>>>>>>>>>>>>>>>>>-------- %d\n", i + 1);
		m[ARRAY_SIZE - 1][ARRAY_SIZE - 1] = interchange(m, i, n);
		display(m, n);
		printf("\n_______________________________________\n");
		m[ARRAY_SIZE - 1][ARRAY_SIZE - 1] = eliminate(m, i, n);
		display(m, n);
	}
	printf("\n\n Values are : \n");
	for (i = n - 1; i >= 0; i--)
	{
		l = n - 1;
		mul = 0;
		for (j = 0; j < k; j++)
		{
			mul = mul + m[i][l] * ans[l];
			l--;
		}
		k++;
		ans[i] = (m[i][n] - mul) / m[i][i];
		printf("X%d = %.2f\n", i + 1, ans[i]);
	}

	return 0;
}