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chi2

gammapy.stats.chi2(N_S, B, S, sigma2)

Chi-square statistic with user-specified variance.

$$\chi^2 = \frac{(N_S - B - S) ^ 2}{\sigma ^ 2}$$

Parameters:

N_S : array_like

Number of observed counts

B : array_like

Model background

S : array_like

Model signal

sigma2 : array_like

Variance

Returns:

stat : ndarray

Statistic per bin

References

• Sherpa stats page (http://cxc.cfa.harvard.edu/sherpa/statistics/#chisq)