cash

gammapy.stats.cash(n_on, mu_on, truncation_value=1e-25)

Cash statistic, for Poisson data.

The Cash statistic is defined as:

\[C = 2 \left( \mu_{on} - n_{on} \log \mu_{on} \right)\]

and \(C = 0\) where \(\mu <= 0\). For more information see Fit statistics

Parameters

n_onarray_like

Observed counts

mu_onarray_like

Expected counts

truncation_valuearray_like

Minimum value use for mu_on mu_on = truncation_value where mu_on <= truncation_value Default is 1e-25.

Returns

statndarray

Statistic per bin

References

• Sherpa statistics page section on the Cash statistic

• Sherpa help page on the Cash statistic

• Cash 1979, ApJ 228, 939