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_onndarray or array_like

Observed counts.

mu_onndarray or array_like

Expected counts.

truncation_valuendarray or array_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,