Fitting - minor bugs and possible tweaks

[ianan]

Provide a general description of the issue or problem.

Testing the fitting for a variety of NuSTAR sources and finding similar results to XSPEC . But also finding a number of inconsistencies, minor bugs and things that need tweaked:

• For default plotting y-axis label is wrong - not a "Count Spectrum [cts/s/keV]" as units count/s/keV. Just change label to units, i.e. count/s/keV?
• For default plotting, add option to turn off annotate plot with fit results, i.e. _plot_params in https://github.com/sunpy/sunxspex/blob/818ae4f7f47db1c3049f02a57a2aaf8ea2eac963/sunxspex/sunxspex_fitting/fitter.py#L3005
• Can easily extract spectrum and fits for own manual plotting but:
  • resid=spec.plotting_info['spectrum1']['residuals'] doesn't return the residuals, but a modified version of them for the internal plotting - every element repeated so need to do spec.plotting_info['spectrum1']['residuals'][::2].
  • Naming of things a bit inconsistent particularly in terms of plurals, i.e. counts, count_rates, count_channel_error, count_rate_errors.
  • Also have count_rate in loaded_spec_data but count_rates in plotting_info.
  • What is called count_rates (and count_rate) is actually count/s/keV - probably call it flux though flux usually count/s/keV/cm2?
  • It would help if each had a descriptor saving what they are, or include actual units?
• Not clear the units/scaling of the fit parameters. So add descriptor or units when returning something like spec.params["T1_spectrum1"]?
  • Also confusing fit uses different thermal params from actual model thermal.thermal_emission, i.e. MK and 1e26 cm^-3 against keV and cm^-3. Is this something to do with fit optimisation?
• Need a simpler (and more) examples, just doing basic fit but also show how to extract fit params and other stuff.

[settwi]

i think these are really good points--refactor should make things clearer.
keeping units attached to the model parameters might be the best way to do that but also might slow things down.