fitting: xarray now provides a curvefit wrapper

[pbeaucage]

see https://xarray.pydata.org/en/stable/generated/xarray.DataArray.curvefit.html
also https://xarray.pydata.org/en/stable/generated/xarray.DataArray.polyfit.html

@dsunday might be interested in this. I have not looked into it in any depth, but seemed worth noting.

[EliotGann]

example use of this from beamtime today:

data = c[-1]['primary']['data'].read()
data = data.assign_coords(coords={'m3pitch':data['SST 1 Mirror 3 fmb_pitch_setpoint'],'energy':data['en_energy_setpoint']}).swap_dims({'time':'system'}).set_index({'system':['m3pitch','energy']}).unstack('system')#.reset_index('time',drop=True).unstack('system')
m3peakpos = data['SAXS Beamstop'].curvefit('m3pitch',gauss_function).sel(param='x0').curvefit_coefficients

def gauss_function(x, a, x0, sigma):
return anp.exp(-(x-x0)**2/(2sigma**2))