cash#

gammapy.stats.cash(n_on, mu_on, truncation_value=1e-25)[source]#

Cash statistic, for Poisson data.

The Cash statistic is defined as:

$$C=2({\mu }_{on}-n_{on}\log {\mu }_{on})$$

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,