cash

gammapy.stats.cash(n_on, mu_on)

Cash statistic, for Poisson data.

The Cash statistic is defined as:

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

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

Parameters:

n_on : array_like

Observed counts

mu_on : array_like

Expected counts

Returns:

stat : ndarray

Statistic per bin

References

• Sherpa statistics page section on the Cash statistic
• Sherpa help page on the Cash statistic
• Cash 1979, ApJ 228, 939