Cholesky Factorization in C?

Question

I am implementing the Cholesky Method in C but the program quits when it arrives at this point.

After the answers : Now it works thanks to the answers of (devnull & piotruś) but it doens't give me the right answer

/* Ax=b
 *This algorithm does:
 *   A = U * U' 
 * with
 *   U  := lower left triangle matrix
 *   U' := the transposed form of U.
 */

double** cholesky(double **A, int N) //this gives me the U (edited)
{
    int i, j, k;
    double sum, **p, **U;
    U=(double**)malloc(N*sizeof(double*));
    for(p=U; p<U+N; p++)
        *p=(double*)malloc(N*sizeof(double));
    for (j=0; j<N; j++) {
        sum = A[j][j];
        for (k=0; k<(j-1); k++) sum -= U[k][j]*U[k][j];
            U[j][j] = sqrt(sum);
            for (i=j; i<N; i++) {
                sum = A[j][i];
                for (k=0; k<(j-1); k++)
                    sum -= U[k][j]*U[k][i];
                U[j][i] = sum/U[j][j];
            }
    }
return U;
}

am I doing something wrong here?

Answer 1

double** cholesky(double **A, int N)

in this function you assume array length is N. This means the last index of array is at N-1 not at N. Change the code into:

for ( j = 0; j < N; ++j)

and the rest similarly.