C Find sub-symmetric matrix in one big matrix - c

Question

I try to find all the sub-symmetric matrix in one big matrix but I only get some of the sub-symmetric matrix and some of them are incorrect.
In my function I found all the sub-matrix and try to send all the square sub-matrix to function that check if the sub-matrix is symmetric, If the sub-matrix is symmetric I print the matrix.
main -
int main() {
int matrix[][8] = {{1, 2, 0, 3, 2, 1, 0, 9},
{2, 3, 4, 1, 2, 3, 4, 5},
{3, 4, 6, 2, 5, 6, 7, 86},
{9, 5, 8, 3, 6, 8, 9, 8},
{6, 7, 1, 4, 7, 9, 1, 9}};
findSubMatrix(matrix, 5, 8);
return 0;
}
findSubMatrix -
void findSubMatrix(int matrix[][8], int rows, int cols) {
for (int i = 0; i <= cols; i++) {
for (int j = i; j <= cols; j++) {
for (int m = 0; m <= rows; m++) {
for (int n = m; n <= rows; n++) {
if (n - m == j - i && n - m > 0) {
if (isSymmetric(matrix, i, j, m, n) == 1) {
for (int k = m; k <= n; k++) {
for (int l = i; l <= j; l++) {
printf("%d ", matrix[k][l]);
}
printf("\n");
}
printf("\n");
}
}
}
}
}
}
}
isSymmetric -
int isSymmetric(int matrix[][8], int rowStart, int rowEnd, int colStart, int colEnd) {
for (int i = colStart; i < colEnd; i++) {
for (int j = rowStart; j < rowEnd; j++) {
if (matrix[j][i] != matrix[i][j]) {
return -1;
}
}
}
return 1;
}
I appreciate any help Thanks.

Answer 1

All the sub-matrices, whether are they beeing tested or printed, should be square, so I'd use a different signature than OP's. Take for example this helper function which prints out a sub-matrix, given a bigger matrix passed with VLA notation, a starting point (indices of the top left corner) and a size:
void print_submatrix(int cols, int m[][cols],
int first_row, int first_col, int n)
{
for (int r = 0; r < n; ++r) {
for (int c = 0; c < n; ++c) {
printf("%3d", m[first_row + r][first_col + c]);
}
putchar('\n');
}
putchar('\n');
}
This should help us finding the correct formulas to evaluate the indices in the function that checks symmetry.
int is_symmetric(int cols, int matrix[][cols],
int first_row, int first_col, int n)
{
for (int i = 0; i < n; ++i) {
for (int j = i + 1; j < n; ++j) {
// ^^^^^^^^^ I'll loop only through half the sub-matrix
if ( matrix[first_row + i][first_col + j]
!= matrix[first_row + j][first_col + i] ) {
// ^^^^^^^^^^^^^ ^^^^^^^^^^^^^
// Note that the starting point (top left corner) is fixed,
// while the offset is changing
return 0;
}
}
}
return 1;
}
The outer loops could be rewritten too
void find_sym_submatrices(int rows, int cols, int matrix[][cols])
{
// For every possible top left corner...
for (int i = 0, mi = rows; i < rows; ++i, --mi) {
for (int j = 0, mj = cols; j < cols; j++, --mj) {
// For every possible square matrix (which fits in size).
const int m = mj < mi ? mj : mi;
for (int n = 2; n <= m; ++n) {
if (is_symmetric(cols, matrix, i, j, n) == 1) {
print_submatrix(cols, matrix, i, j, n);
}
else {
break; // Yeap, there's no need to check the bigger ones.
}
}
}
}
}
Live, here.