Question

Write a GLM function named getInverse that returns the inverse of A. If A does not have an inverse, the function returns the identify matrix. Assume A is 3x3.

Answer 1

#include<stdio.h>
#include<math.h>
float determinant(float [][25], float);
void cofactor(float [][25], float);
void transpose(float [][25], float [][25], float);
int main()
{
float a[25][25], k = 3 , d;
int i, j;
  
// here you can make matric size dynamic by comment these 2 lines below it.
  
// printf("Enter the order of the Matrix : ");
// scanf("%f", &k);
printf("Enter the elements of %.0fX%.0f Matrix : \n", k, k);
for (i = 0;i < k; i++)
{
for (j = 0;j < k; j++)
{
scanf("%f", &a[i][j]);
}
}
d = determinant(a, k);
if (d == 0){
   printf("\nInverse of Entered Matrix is not possible, Identity matric is : \n \n");
     
}
else
cofactor(a, k);
}

// print identity matric
int Identity(int num)
{
int row, col;
  
for (row = 0; row < num; row++)
{
for (col = 0; col < num; col++)
{
// Checking if row is equal to column
if (row == col)
   printf("1 ");
else
printf("0 ");
}
printf("\n");
}
return 0;
}

/*For calculating Determinant of the Matrix */
float determinant(float a[25][25], float k)
{
float s = 1, det = 0, b[25][25];
int i, j, m, n, c;
if (k == 1)
{
return (a[0][0]);
}
else
{
det = 0;
for (c = 0; c < k; c++)
{
m = 0;
n = 0;
for (i = 0;i < k; i++)
{
for (j = 0 ;j < k; j++)
{
b[i][j] = 0;
if (i != 0 && j != c)
{
b[m][n] = a[i][j];
if (n < (k - 2))
n++;
else
{
n = 0;
m++;
}
}
}
}
det = det + s * (a[0][c] * determinant(b, k - 1));
s = -1 * s;
}
}

return (det);
}

void cofactor(float num[25][25], float f)
{
float b[25][25], fac[25][25];
int p, q, m, n, i, j;
for (q = 0;q < f; q++)
{
for (p = 0;p < f; p++)
{
m = 0;
n = 0;
for (i = 0;i < f; i++)
{
for (j = 0;j < f; j++)
{
if (i != q && j != p)
{
b[m][n] = num[i][j];
if (n < (f - 2))
n++;
else
{
n = 0;
m++;
}
}
}
}
fac[q][p] = pow(-1, q + p) * determinant(b, f - 1);
}
}
transpose(num, fac, f);
}
/*Finding transpose of matrix*/
void transpose(float num[25][25], float fac[25][25], float r)
{
int i, j;
float b[25][25], inverse[25][25], d;

for (i = 0;i < r; i++)
{
for (j = 0;j < r; j++)
{
b[i][j] = fac[j][i];
}
}
d = determinant(num, r);
for (i = 0;i < r; i++)
{
for (j = 0;j < r; j++)
{
inverse[i][j] = b[i][j] / d;
}
}
printf("\n\n\nThe inverse of matrix is : \n");

for (i = 0;i < r; i++)
{
for (j = 0;j < r; j++)
{
printf("\t%f", inverse[i][j]);
}
printf("\n");
}
}

// Happy Hack :)