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cash

gammapy.stats.cash(n_on, mu_on)

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_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