cstat#

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

C statistic, for Poisson data.

The C statistic is defined as:

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

and $C=0$ where ${\mu }_{on}<=0$.

truncation_value handles the case where n_on or mu_on is 0 or less and the log cannot be taken. For more information see Fit statistics.

Parameters:

n_onndarray or array_like

Observed counts.

mu_onndarray or array_like

Expected counts.

truncation_valuefloat

n_on = truncation_value where n_on <= truncation_value. mu_on = truncation_value where n_on <= truncation_value Default is 1e-25.

Returns:

statndarray

Statistic per bin.

References

• Sherpa stats page section on the C statistic:

• Sherpa help page on the C statistic:

• Cash 1979, ApJ 228, 939,