def intensity_perpendicular_from_monomer(M, A_1, A_2, b, c_b_1):
    """
    Calculate perpendicular intesity from monomer fraction, monomer and dimer
    anisotropy, brightness relation and monomer brightness.
    """
    return (1/3)*(((1-A_1) - (1-A_2)*b) *M + (1-A_2)*b)*c_b_1