def dli(x, y, x1, x2, y1, y2, m11, m12, m21, m22):
    """Double Linear Interpolation"""
    first_xs = (x2 - x) / (x2 - x1)
    second_xs = (x - x1) / (x2 - x1)
    first_ys = (y2 - y) / (y2 - y1)
    second_ys = (y - y1) / (y2 - y1)
    m11 *= first_xs
    m12 *= second_xs
    m21 *= first_xs
    m22 *= second_xs
    return (m11 + m12) * first_ys + (m21 + m22) * second_ys
