A custom model in astromodels

my_model.py

from astromodels.functions.function import Function1D, FunctionMeta

class MyCustomModel(Function1D):
    r"""
    description :
        A custom power law model
    latex : $ 10^{K}~\frac{x}{piv}^{index} $
    parameters :
        K :
            desc : Normalization (log of differential flux at the pivot value)
            initial value : 1.0
            is_normalization : True
            transformation : log10
        piv :
            desc : Pivot value
            initial value : 1
            fix : yes
        index :
            desc : Photon index
            initial value : -2
            min : -10
            max : 10
    """

    __metaclass__ = FunctionMeta

    def _set_units(self, x_unit, y_unit):

        # The index is always dimensionless
        self.index.unit = astropy_units.dimensionless_unscaled

        # The pivot energy has always the same dimension as the x variable
        self.piv.unit = x_unit

        # The normalization has the same units as the y

        self.K.unit = y_unit

    # noinspection PyPep8Naming
    def evaluate(self, x, K, piv, index):

        xx = x / piv

        return 10**K * xx**index