fit_function - function component names separated by '+', e.g. 'vth+bpow'. The output is the sum of each function component computed at each energy in fit_xvals.
List of Function Components
fit_xvals - energy edges in keV as 2,n array
fit_comp_params - dimensioned to the sum of the number of parameters for each component
fit_comp_spectrum - options are 'full', 'continuum', or 'lines', default is 'full', dimensioned to the number of function components
fit_comp_model - options are 'chianti' or 'mewe', default is 'chianti', dimensioned to the number of function components
fit_comp_spectrum and fit_comp_model apply only to thermal functions, and are blank for non-thermal components
For example for a multi_therm_pow+line function, you would have something like:
fit_comp_params=[.005, .5, 4., 1., 1., 1000., 6.7, .1] where the first 5 values are for multi_therm_pow and the next 3 for line
fit_comp_spectrum=['continuum', ''] where the first string applies to multi_therm_pow, and the second (null) string applies to the line function
Note: the fit_comp_function parameter should not be set by the user. It is set internally to an array of the function component names corresponding to the names in the fit_function parameter string.