XMM-Newton Science Analysis System


ssclib (ssclib-3.24) [xmmsas_20050815_1803-6.5.0]

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$\chi ^2$ probability

This subroutine gives the probability that a given reduced $\chi ^2$ (ie, $\chi ^2$/degFree) is `natural' - ie it gives the probability of the null hypothesis. $\chi ^2$ is defined as follows:

$$\chi^2 = \frac{\sum_{i=1}^{N-1} (y_i - f_i)^2}{\sigma_{y_i}^{2}}$$

where $y_i$ is the measured or data value, $f_i$ is the model or expected value and $\sigma_{y_i}$ is the uncertainty in the data.

  subroutine chi2Prob(chi2, degFree, probability, status)
    real(single), intent(in)            :: chi2
    integer,      intent(in)            :: degFree
    real(single), intent(out)           :: probability
    integer,      intent(out), optional :: status
  end subroutine chi2Prob