Fix #206 by performing numerical differentiation of the gabs and the other multiplicative models which need it
Fix #206 by performing numerical differentiation of the gabs and the other multiplicative models which need it

giacomov/astromodels,giacomov/astromodels,grburgess/astromodels,grburgess/astromodels,giacomov/astromodels,grburgess/astromodels