code: def get_residuals(ds, m):
      
      model_spectra = get_model_spectra(ds, m)
      resid = ds.test_flux - model_spectra
      return resid
docs: Using the dataset and model object, calculate the residuals and return
  
      Parameters
      ----------
      ds: dataset object
      m: model object
      Return
      ------
      residuals: array of residuals, spec minus model spec