def matrix_subtraction(a, b):
    """matrix_subtraction
    Matrix subtraction a[i][j]-b[i][j] for all i j
    :param a: first matrix
    :param b: second matrix
    :return: first-second result
    """
    c = [[0 for y in range(len(a[0]))] for x in range(len(a))]
    for i in range(len(a)):
        for j in range(len(a[0])):
            c[i][j] = a[i][j] - b[i][j]
    return c