Matrix inverse in C [req]

[anoop12]

c program to find inverse of a matrix

hello everyone,
I am trying to write C program to find inverse of a matrix.
Do anyone have it?
Thanks

 

[aospinas]

c program to find the inverse of a matrix

use numerical recipes in C!!!

enjoy

 

[prakashrtvm]

matrix inverse in c

Hope This will help...

/************************************************************************/
/* Please Note: */
/* */
/* (1) This computer program is written by Tao Pang in conjunction with */
/* his book, "An Introduction to Computational Physics," published */
/* by Cambridge University Press in 1997. */
/* */
/* (2) No warranties, express or implied, are made for this program. */
/* */
/************************************************************************/

#include <stdio.h>
#include <math.h>
#define NMAX 100

void migs (a,n,x,indx)

/* Function to invert matrix a[][] with the inverse stored
in x[][] in the output. Copyright (c) Tao Pang 2001. */
int n;
int indx[];
double a[NMAX][NMAX],x[NMAX][NMAX];
{
int i,j,k;
double b[NMAX][NMAX];
void elgs();

if (n > NMAX)
{
printf("The matrix dimension is too large.\n");
exit(1);
}

for (i = 0; i < n; ++i)
{
for (j = 0; j < n; ++j)
{
b[j] = 0;
}
}
for (i = 0; i < n; ++i)
{
b = 1;
}

elgs (a,n,indx);

for (i = 0; i < n-1; ++i)
{
for (j = i+1; j < n; ++j)
{
for (k = 0; k < n; ++k)
{
b[indx[j]][k] = b[indx[j]][k]-a[indx[j]]*b[indx][k];
}
}
}

for (i = 0; i < n; ++i)
{
x[n-1] = b[indx[n-1]]/a[indx[n-1]][n-1];
for (j = n-2; j >= 0; j = j-1)
{
x[j] = b[indx[j]];
for (k = j+1; k < n; ++k)
{
x[j] = x[j]-a[indx[j]][k]*x[k];
}
x[j] = x[j]/a[indx[j]][j];
}
}
}

void elgs (a,n,indx)

/* Function to perform the partial-pivoting Gaussian elimination.
a[][] is the original matrix in the input and transformed
matrix plus the pivoting element ratios below the diagonal
in the output. indx[] records the pivoting order.
Copyright (c) Tao Pang 2001. */

int n;
int indx[];
double a[NMAX][NMAX];
{
int i, j, k, itmp;
double c1, pi, pi1, pj;
double c[NMAX];

if (n > NMAX)
{
printf("The matrix dimension is too large.\n");
exit(1);
}

/* Initialize the index */

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

/* Find the rescaling factors, one from each row */

for (i = 0; i < n; ++i)
{
c1 = 0;
for (j = 0; j < n; ++j)
{
if (fabs(a[j]) > c1) c1 = fabs(a[j]);
}
c = c1;
}

/* Search the pivoting (largest) element from each column */

for (j = 0; j < n-1; ++j)
{
pi1 = 0;
for (i = j; i < n; ++i)
{
pi = fabs(a[indx][j])/c[indx];
if (pi > pi1)
{
pi1 = pi;
k = i;
}
}

/* Interchange the rows via indx[] to record pivoting order */

itmp = indx[j];
indx[j] = indx[k];
indx[k] = itmp;
for (i = j+1; i < n; ++i)
{
pj = a[indx][j]/a[indx[j]][j];

/* Record pivoting ratios below the diagonal */

a[indx][j] = pj;

/* Modify other elements accordingly */

for (k = j+1; k < n; ++k)
{
a[indx][k] = a[indx][k]-pj*a[indx[j]][k];
}
}
}