fit_comp_minima , fit_comp_maxima - limits the range of values for each parameter
fit_comp_free_mask - 0 or 1 indicating whether the parameter is fixed, or free to vary during fitting
For example for a multi_therm_pow+line function, you would set values like this:
fit_comp_minima=[1.e-10, .5, 1., .01, .01, 1.e-20, 1., .01]
fit_comp_free_mask=[1, 0, 1, 1, 0, 1, 0, 0]
where the first 5 values are for multi_therm_pow and the next 3 for line