int
printf(const char *, ...);

void
initGeMatrix(int m, int n, double *A, int incRowA, int incColA)
{
    int i, j;

    for (i=0; i<m; ++i) {
        for (j=0; j<n; ++j) {
            A[i*incRowA+j*incColA] = i*n + j + 1;
        }
    }
}

void
printGeMatrix(int m, int n, const double *A, int incRowA, int incColA)
{
    int i, j;

    for (i=0; i<m; ++i) {
        for (j=0; j<n; ++j) {
            printf("%10.4lf ", A[i*incRowA+j*incColA]);
        }
        printf("\n");
    }
    printf("\n\n");
}

double A[6*8];

int
main()
{
    initGeMatrix(6, 8, A, 1, 6);

    printf("A =\n");
    printGeMatrix(6, 8, A, 1, 6);

    printf("A^T =\n");
    printGeMatrix(8, 6, A, 6, 1);

    printf("diag(A) =\n");
    printGeMatrix(6, 1, A, 1+6, 6);

    return 0;
}