def find_max(a):
    """
    Find the coordinates (i0, j0) in terms of pixels of the maximum correlation peak from
    the polynomial surface fit parameters

    :param a: List of polynomial surface fit parameters returned by polyfit2d()

    Returns i0, j0
    """

    i0 = ((a[2]*a[3]) - (2*a[0]*a[4])) / (4*a[0]*a[1] - a[2]**2)
    j0 = ((a[2] * a[4]) - (2 * a[1] * a[3])) / (4 * a[0] * a[1] - a[2] ** 2)

    return i0, j0