DZone Snippets: elimination code

Gaussian Elimination in C

scvalex (Alexandru Scvortov) — Tue, 11 Dec 2007 13:46:27 GMT

This is a simple implementation of the Gaussian Elimination algorithm for solving n linear equations with n unknowns.

Further explanation is given here.



#include 



int n;

float a[10][11];



void forwardSubstitution() {

	int i, j, k, max;

	float t;

	for (i = 0; i < n; ++i) {

		max = i;

		for (j = i + 1; j < n; ++j)

			if (a[j][i] > a[max][i])

				max = j;

		

		for (j = 0; j < n + 1; ++j) {

			t = a[max][j];

			a[max][j] = a[i][j];

			a[i][j] = t;

		}

		

		for (j = n; j >= i; --j)

			for (k = i + 1; k < n; ++k)

				a[k][j] -= a[k][i]/a[i][i] * a[i][j];



/*		for (k = 0; k < n; ++k) {

			for (j = 0; j < n + 1; ++j)

				printf("%.2f\t", a[k][j]);

			printf("\n");

		}*/

	}

}



void reverseElimination() {

	int i, j;

	for (i = n - 1; i >= 0; --i) {

		a[i][n] = a[i][n] / a[i][i];

		a[i][i] = 1;

		for (j = i - 1; j >= 0; --j) {

			a[j][n] -= a[j][i] * a[i][n];

			a[j][i] = 0;

		}

	}

}



void gauss() {

	int i, j;



	forwardSubstitution();

	reverseElimination();

	

	for (i = 0; i < n; ++i) {

		for (j = 0; j < n + 1; ++j)

			printf("%.2f\t", a[i][j]);

		printf("\n");

	}

}



int main(int argc, char *argv[]) {

	int i, j;



	FILE *fin = fopen("gauss.in", "r");

	fscanf(fin, "%d", &n);

	for (i = 0; i < n; ++i)

		for (j = 0; j < n + 1; ++j)

			fscanf(fin, "%f", &a[i][j]);

	fclose(fin);

	

	gauss();

	

	return 0;

}

Gaussian Elimination in C

scvalex (Alexandru Scvortov) — Tue, 11 Dec 2007 13:46:02 GMT

This is a simple implementation of the Gaussian Elimination algorithm for solving n linear equations with n unknowns.

Further explanation is given here.



#include 



int n;

float a[10][11];



void forwardSubstitution() {

	int i, j, k, max;

	float t;

	for (i = 0; i < n; ++i) {

		max = i;

		for (j = i + 1; j < n; ++j)

			if (a[j][i] > a[max][i])

				max = j;

		

		for (j = 0; j < n + 1; ++j) {

			t = a[max][j];

			a[max][j] = a[i][j];

			a[i][j] = t;

		}

		

		for (j = n; j >= i; --j)

			for (k = i + 1; k < n; ++k)

				a[k][j] -= a[k][i]/a[i][i] * a[i][j];



/*		for (k = 0; k < n; ++k) {

			for (j = 0; j < n + 1; ++j)

				printf("%.2f\t", a[k][j]);

			printf("\n");

		}*/

	}

}



void reverseElimination() {

	int i, j;

	for (i = n - 1; i >= 0; --i) {

		a[i][n] = a[i][n] / a[i][i];

		a[i][i] = 1;

		for (j = i - 1; j >= 0; --j) {

			a[j][n] -= a[j][i] * a[i][n];

			a[j][i] = 0;

		}

	}

}



void gauss() {

	int i, j;



	forwardSubstitution();

	reverseElimination();

	

	for (i = 0; i < n; ++i) {

		for (j = 0; j < n + 1; ++j)

			printf("%.2f\t", a[i][j]);

		printf("\n");

	}

}



int main(int argc, char *argv[]) {

	int i, j;



	FILE *fin = fopen("gauss.in", "r");

	fscanf(fin, "%d", &n);

	for (i = 0; i < n; ++i)

		for (j = 0; j < n + 1; ++j)

			fscanf(fin, "%f", &a[i][j]);

	fclose(fin);

	

	gauss();

	

	return 0;

}

Gaussian Elimination in C

scvalex (Alexandru Scvortov) — Tue, 11 Dec 2007 13:45:52 GMT

This is a simple implementation of the Gaussian Elimination algorithm for solving n linear equations with n unknowns.

Further explanation is given here.



#include 



int n;

float a[10][11];



void forwardSubstitution() {

	int i, j, k, max;

	float t;

	for (i = 0; i < n; ++i) {

		max = i;

		for (j = i + 1; j < n; ++j)

			if (a[j][i] > a[max][i])

				max = j;

		

		for (j = 0; j < n + 1; ++j) {

			t = a[max][j];

			a[max][j] = a[i][j];

			a[i][j] = t;

		}

		

		for (j = n; j >= i; --j)

			for (k = i + 1; k < n; ++k)

				a[k][j] -= a[k][i]/a[i][i] * a[i][j];



/*		for (k = 0; k < n; ++k) {

			for (j = 0; j < n + 1; ++j)

				printf("%.2f\t", a[k][j]);

			printf("\n");

		}*/

	}

}



void reverseElimination() {

	int i, j;

	for (i = n - 1; i >= 0; --i) {

		a[i][n] = a[i][n] / a[i][i];

		a[i][i] = 1;

		for (j = i - 1; j >= 0; --j) {

			a[j][n] -= a[j][i] * a[i][n];

			a[j][i] = 0;

		}

	}

}



void gauss() {

	int i, j;



	forwardSubstitution();

	reverseElimination();

	

	for (i = 0; i < n; ++i) {

		for (j = 0; j < n + 1; ++j)

			printf("%.2f\t", a[i][j]);

		printf("\n");

	}

}



int main(int argc, char *argv[]) {

	int i, j;



	FILE *fin = fopen("gauss.in", "r");

	fscanf(fin, "%d", &n);

	for (i = 0; i < n; ++i)

		for (j = 0; j < n + 1; ++j)

			fscanf(fin, "%f", &a[i][j]);

	fclose(fin);

	

	gauss();

	

	return 0;

}