code: def f_cash(x, counts, bkg, model):
      
  
      return 2.0 * poisson_log_like(counts, bkg + x * model)
docs: Wrapper for cash statistics, that defines the model function.
  
      Parameters
      ----------
      x : float
          Model amplitude.
      counts : `~numpy.ndarray`
          Count map slice, where model is defined.
      bkg : `~numpy.ndarray`
          Background map slice, where model is defined.
      model : `~numpy.ndarray`
          Source template (multiplied with exposure).