Chi2ConstVar¶
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class
sherpa.stats.
Chi2ConstVar
(name='chi2constvar')[source] [edit on github]¶ Bases:
sherpa.stats.Chi2
Chi Squared with constant variance.
The variance is the same in each bin, and set to be the mean number of counts in the data:
sigma(i)^2 = (1/N) * (sum)_(j=1)^N N(j,S) + [A(S)/A(B)]^2 N(j,B)where N is the number of on-source (and off-source) bins included in the fit. The background term appears only if an estimate of the background has been subtracted from the data.
Methods Summary
calc_chisqr
(data, model)Return the chi-square value for each bin. calc_stat
(data, model)Return the statistic value for the data and model. calc_staterror
(data)Return the statistic error values for the data. goodness_of_fit
(statval, dof)Return the reduced statistic and q value. Methods Documentation
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calc_chisqr
(data, model) [edit on github]¶ Return the chi-square value for each bin.
Parameters: - data (a Data or DataSimulFit instance) – The data set, or sets, to use.
- model (a Model or SimulFitModel instance) – The model expression, or expressions. If a SimulFitModel is given then it must match the number of data sets in the data parameter.
Returns: chisqr – The per-bin chi-square values.
Return type: array of numbers
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calc_stat
(data, model) [edit on github]¶ Return the statistic value for the data and model.
Parameters: - data (a Data or DataSimulFit instance) – The data set, or sets, to use.
- model (a Model or SimulFitModel instance) – The model expression, or expressions. If a SimulFitModel is given then it must match the number of data sets in the data parameter.
Returns: statval, fvec – The statistic value and the per-bin “statistic” value.
Return type: number, array of numbers
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static
calc_staterror
(data)[source] [edit on github]¶ Return the statistic error values for the data.
Parameters: data (scalar or 1D array of numbers) – The data values. Returns: staterror – The errors for the input data values (matches the data argument). Return type: scalar or array of numbers
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goodness_of_fit
(statval, dof) [edit on github]¶ Return the reduced statistic and q value.
The reduced statisitc is conceptually simple, as it is just statistic / degrees-of-freedom, but it is not meaningful for all statistics, and it is only valid if there are any degrees of freedom.
Parameters: - statval (float) – The statistic value. It is assumed to be finite.
- dof (int) – The number of degrees of freedom, which may be 0 or negative.
Returns: rstat, qval – The reduced statistic and q value. If the statistic does not support a goodness of fit then the return values are None. If it does then NaN is returned if either the number of degrees of freedom is 0 (or less), or the statistic value is less than 0.
Return type: float or NaN or None, float or NaN or None
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