Chi2ConstVar
- class sherpa.stats.Chi2ConstVar(name='chi2constvar')[source] [edit on github]
Bases:
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/K) * (sum)_(j=1)^K N(j,S) + [A(S)/A(B)]^2 N(j,B)
where K 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
- calc_chisqr(data, model) [edit on github]
Return the chi-square value for each bin.
- Parameters
data (
sherpa.data.Data
orsherpa.data.DataSimulFit
) – The data set, or sets, to use.model (
sherpa.models.model.Model
orsherpa.models.model.SimulFitModel
) – The model expression, or expressions. If asherpa.models.model.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
- calc_stat(data, model) [edit on github]
Return the statistic value for the data and model.
- Parameters
data (
sherpa.data.Data
orsherpa.data.DataSimulFit
) – The data set, or sets, to use.model (
sherpa.models.model.Model
orsherpa.models.model.SimulFitModel
) – The model expression, or expressions. If asherpa.models.model.SimulFitModel
is given then it must match the number of data sets in the data parameter.
- Returns
statval (number) – The value of the statistic.
fvec (array of numbers) – The per-bin “statistic” value.
- 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
- 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
- Returns
rstat (float or NaN or None) – The reduced statistic. If the statistic does not support a goodness of fit then the return value is
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.qval (float or NaN or None) – The 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.