xgaussj.c

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/* Driver for routine gaussj */

#include <stdio.h>
#include <stdlib.h>
#define NRANSI
#include "nr.h"
#include "nrutil.h"

#define NP 20
#define MP 20
#define MAXSTR 80

int main(void)
{
	int j,k,l,m,n;
	float **a,**ai,**u,**b,**x,**t;
	char dummy[MAXSTR];
	FILE *fp;

	a=matrix(1,NP,1,NP);
	ai=matrix(1,NP,1,NP);
	u=matrix(1,NP,1,NP);
	b=matrix(1,NP,1,MP);
	x=matrix(1,NP,1,MP);
	t=matrix(1,NP,1,MP);
	if ((fp = fopen("matrx1.dat","r")) == NULL)
		nrerror("Data file matrx1.dat not found\n");
	while (!feof(fp)) {
		fgets(dummy,MAXSTR,fp);
		fgets(dummy,MAXSTR,fp);
		fscanf(fp,"%d %d ",&n,&m);
		fgets(dummy,MAXSTR,fp);
		for (k=1;k<=n;k++)
			for (l=1;l<=n;l++) fscanf(fp,"%f ",&a[k][l]);
		fgets(dummy,MAXSTR,fp);
		for (l=1;l<=m;l++)
			for (k=1;k<=n;k++) fscanf(fp,"%f ",&b[k][l]);
		/* save matrices for later testing of results */
		for (l=1;l<=n;l++) {
			for (k=1;k<=n;k++) ai[k][l]=a[k][l];
			for (k=1;k<=m;k++) x[l][k]=b[l][k];
		}
		/* invert matrix */
		gaussj(ai,n,x,m);
		printf("\nInverse of matrix a : \n");
		for (k=1;k<=n;k++) {
			for (l=1;l<=n;l++) printf("%12.6f",ai[k][l]);
			printf("\n");
		}
		/* check inverse */
		printf("\na times a-inverse:\n");
		for (k=1;k<=n;k++) {
			for (l=1;l<=n;l++) {
				u[k][l]=0.0;
				for (j=1;j<=n;j++)
					u[k][l] += (a[k][j]*ai[j][l]);
			}
			for (l=1;l<=n;l++) printf("%12.6f",u[k][l]);
			printf("\n");
		}
		/* check vector solutions */
		printf("\nCheck the following for equality:\n");
		printf("%21s %14s\n","original","matrix*sol'n");
		for (l=1;l<=m;l++) {
			printf("vector %2d: \n",l);
			for (k=1;k<=n;k++) {
				t[k][l]=0.0;
				for (j=1;j<=n;j++)
					t[k][l] += (a[k][j]*x[j][l]);
				printf("%8s %12.6f %12.6f\n"," ",
					b[k][l],t[k][l]);
			}
		}
		printf("***********************************\n");
		printf("press RETURN for next problem:\n");
		(void) getchar();
	}
	fclose(fp);
	free_matrix(t,1,NP,1,MP);
	free_matrix(x,1,NP,1,MP);
	free_matrix(b,1,NP,1,MP);
	free_matrix(u,1,NP,1,NP);
	free_matrix(ai,1,NP,1,NP);
	free_matrix(a,1,NP,1,NP);
	return 0;
}
#undef NRANSI