Hello
I am trying to write a matrix calculator but I have some problems.I use cofactor method for calculation.If you don't know the this method you can learn it here easily: http://paulbourke.net/miscellaneous/determinant/
I use two function 1- GetMinor() 2- matrixCofactor() that the first one give me the minor matrix and I calculate determinant recursively in matrixCofactor() and print the determinant of the every matrix and its sub matrixes in every step. I don't know where the problem reside but I predict maybe problem be from recursive calls.I attach all my code file but I think this two function is enough for getting what is happening:

``````int GetMinor(Matrix *src,Matrix *dest, int row, int col, int order)
{
// indicate which col and row is being copied to dest

int colCount = 0,rowCount = 0;
int i,j;

for(i = 0; i < order; i++ ){
if( i != row )
{
colCount = 0;
for( j = 0; j < order; j++ )
{
// when j is not the element
if( j != col )
{
dest->elements[rowCount][colCount] = src->elements[i][j];
colCount++;
}
}
rowCount++;
}
}
return 0;
}

int matrixCofact(Matrix* mat,int order,double* determinan){
int i;
Matrix* minor;
minor = malloc(sizeof(double));
newMatrix(order-1,order-1,minor);
double* det;
det = malloc(sizeof(double));
if( order == 1 ){
printf("The End");
}
for(i = 0; i <order;i++){
GetMinor( mat, minor, 0, i, order);
printf("\n");
matrixPrint(minor);
if( minor->colCount > 3){
*det += pow(-1.0,i+0) * minor->elements[i] * matrixCofact(minor,order-1,det);
printf("\nThe matrix determinant is: %f",*det);
}else{
matrix3dDeterminan(minor,det);
printf("\nThe matrix determinant is: %f",*det);
}
}
printf("BYE ");
return 0;
}``````

## All 3 Replies

I don't see anything obvious, but I'm not familiar with this, either.

If I were starting to debug it, I'd probably start with assertions to check that all the indices are staying within their proper ranges. Then start checking the subtotals, and whether j=0 is correct, for it's initialization (or should it be j=i?).
Should newmatrix be set to order-1?, etc.

There are lots of examples of this kind of code, but I don't know if it uses the cofactor method or not.

At line 42 you call matrixCofact as if it returns the minor's determinant. I recommend to (a) make matrixCofact return double, (b) get rid of its third parameter (you don't use it anyway), and (c) change line 50 to `return det` . Of course, det should be just double (not a pointer).
PS: minor->elements at line 52 is wrong. It should be mat->elements.
PPS: You probably know that it is one of the least efficient algorithms.

Hello
nezachem really thanks for your guide it was helpful. Another problem of my code is at line 41:

``if( minor->colCount > 3)``

it should be change to

``if( order <3 )``

because minor row and col amount is 1 less than order at every step because of this code

``newMatrix(order-1,order-1,minor)``
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