cterror

Computes parameter errors for a source model from the likelihood profiles.

Synopsis

This tool computes the parameter errors for a specific source model using the likelihood profiles. Starting from the maximum likelihood model parameters, the tool finds the minimum and maximum model parameters that lead to a decrease of the likelihood that corresponds to a given confidence level. By default a confidence level of 68% is used, but this level can be adjusted using the hidden confidence parameter.

cterror generates an output model XML file that contains the values of the best fitting model parameters. For all free parameters, an error attribute is added that provides the statistical uncertainty in the parameter estimate as obtained from the likelihood profile. While cterror computes asymmetrical errors, which are written into the log file, the XML file will contain the mean error that is obtained by computing the mean of the negative and the positive parameter errors.

In addition, cterror also generates a butterfly based on the parameter errors.

General parameters

inobs [file]

Input event list, counts cube or observation definition XML file.

inmodel [file]

Input model XML file.

srcname [string]

Name of source model for which the parameter errors should be computed.

expcube [file]

Input exposure cube file.

psfcube [file]

Input PSF cube file.

edispcube [file]

Input energy dispersion cube file.

bkgcube [file]

Input background cube file.

caldb [string]

Calibration database.

irf [string]

Instrumental response function.

(edisp = no) [boolean]

Applies energy dispersion to response computation.

outmodel [file]

Output model XML file with updated error information.

outfile [file]

Output butterfly FITS file.

(confidence = 0.68) [real]

Confidence level for error computation.

(tol = 1e-3) [real]

Computation tolerance.

(statistic = DEFAULT) <DEFAULT|CSTAT|WSTAT|CHI2> [string]

Optimization statistic. DEFAULT uses the default statistic for all observations, which is CSTAT or the statistic specified in the observation definition XML file. CSTAT uses the C statistic for all observations, WSTAT uses the W statistic for all On/Off observations, and CHI2 uses the Chi squared statistic for all binned or stacked observations.

(like_accuracy = 0.005) [real]

Absolute accuracy of maximum likelihood value. Reducing this value will increase the number of iterations and provide a more accurate maximum log likelihood value. Converserly, decreasing the value will result in less iterations at the expense of a less accurate maximum likelihood value.

(max_iter = 50) [integer]

Maximum number of iterations before stopping the likelihood profile computations.

(ebinalg = LOG) <FILE|LIN|LOG> [string]

Algorithm for defining energy bins for the butterfly. For FILE, the energy bins are defined in a FITS file that is specified by the ebinfile parameter, for LIN and LOG there will be enumbins energy bins spaced linearly or logarithmically between emin and emax, respectively.

emin [real]

Lower energy value for first energy bin (in TeV) of the buttefly if LIN or LOG energy binning algorithms are used.

emax [real]

Upper energy value for last energy bin (in TeV) of the butterfly if LIN or LOG energy binning algorithms are used.

(enumbins = 100) [integer]

Number of energy bins of the butterfly if LIN or LOG energy binning algorithms are used.

ebinfile [file]

Name of the file containing the energy binning definition if ebinalg=FILE. You may use csebins to generate a file with appropriate energy binning.

Standard parameters

(nthreads = 0) [integer]

Number of parallel processes (0=use all available CPUs).

(chatter = 2) [integer]
Verbosity of the executable:

chatter = 0: no information will be logged

chatter = 1: only errors will be logged

chatter = 2: errors and actions will be logged

chatter = 3: report about the task execution

chatter = 4: detailed report about the task execution

(clobber = yes) [boolean]

Specifies whether an existing output file should be overwritten.

(debug = no) [boolean]

Enables debug mode. In debug mode the executable will dump any log file output to the console.

(mode = ql) [string]

Mode of automatic parameters (default is ql, i.e. “query and learn”).

(logfile = cterror.log) [string]

Name of log file.