Question

Can you tell me which function will work faster? Or perhaps they are both wrong and you know better way to do this. Thanks in advance.

double* solveDiagonal(double* A, double* B, int n)
{
    double* X = new double[n];

    for(int i = 0; i < n; i++)
        X[i] = B[i] / A[i*n + i];

    return X;
}


double* solveDiagonal(double* A, double* B, int n)
{
    double* X = new double[n];
    double** pA = new double*[n];

    for(int i = 0; i < n; i++)
        pA[i] = &A[i*n];

    for(int i = 0; i < n; i++)
        X[i] = B[i] / pA[i][i];

    delete [] pA;

    return X;
}

Answer 1

While I would guess the second one is slower due to more indirection and allocation, you really need to test and profile to answer this kind of question.