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Last modified: December 2013

URL: http://cxc.harvard.edu/sherpa/ahelp/get_covar.html
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AHELP for CIAO 4.9 Sherpa v1

get_covar

Context: confidence

Synopsis

Return settings or results for the covariance method.

Syntax

get_covar()
get_covar_results()
get_covar_opt( [name] )

Description

get_covar

The get_covar command returns the current covariance estimation method object. The function accepts no arguments. The returned information is:

  • sigma - to get 1, 2, or 3-sigma limits, default=1
  • eps - precision of resulting limits, default=0.01
  • maxiters- maximum number of tries to bracket desired limits, before returning, default=200
  • soft_limits - a switch which allows the search to go all the way out to the hard parameter limits; if switched on, the search will be restricted to occur within the soft limits, which can be changed by the user, default=False

get_covar_results

The get_covar_results command accesses results from the last time covariance was run. The function accepts no arguments. The results include the following attributes:

  • datasets - Data sets in fit
  • methodname - Estimation method name
  • fitname - Fitting method name
  • statname - Statistic name
  • percent
  • sigma - Change in statistic
  • parnames - Model parameter names
  • parvals - Model parameter fit values
  • parmins - Model parameter minimum values
  • parmaxes - Model parameter maximum values
  • extra_output - the covariance matrix

get_covar_opt

The get_covar_opt command returns a covariance option by name. If the name isn't specified, it returns a dictionary of all options that govern how covariance is run. The covariance options are modified using the set_covar_opt command.

  • sigma - to get 1, 2, or 3-sigma limits, default=1
  • eps - precision of resulting limits, default=0.01
  • maxiters- maximum number of tries to bracket desired limits, before returning, default=200
  • soft_limits - a switch which allows the search to go all the way out to the hard parameter limits; if switched on, the search will be restricted to occur within the soft limits, which can be changed by the user, default=False

Example 1

sherpa> get_covar()

Return a variable listing of all settings that govern how the covariance method calculates confidence limits. Sample output is

sherpa> print(get_covar())
name        = covariance
soft_limits = False
maxiters    = 200
sigma       = 1
eps         = 0.01

Example 2

sherpa> get_covar_results()

Return a variable listing of all results from the last time covariance was run, e.g.

sherpa> print(get_covar_results())
data sets   = (2,)
methodname = covariance
fitname    = levmar
statname   = chi2gehrels
sigma      = 1
percent    = 68.2689492137
parnames   = ('p2.gamma', 'p2.ampl')
parvals    = (1.0, 1.0)
parmins    = (-2.5123712497785912e-05, -1.8031410361942839e-05)
parmaxes   = (2.5123712497785912e-05, 1.8031410361942839e-05)
nfits      = 0

Example 3

sherpa> get_covar_opt("sigma")
1
sherpa> set_covar_opt("sigma",3)

Return the current value of the covariance sigma option ('1' in this example), and change it to the desired value ('3').

Example 4

sherpa> print get_covar_results().extra_output
[[ 1.00688203e-07 1.94309062e-07 1.63077981e-07 -2.14579320e-08
-2.33234708e-07]
[ 1.94309062e-07 5.97149180e-08 6.14497850e-07 5.95866729e-07
-3.20550581e-07]
[ 1.63077981e-07 6.14497850e-07 1.36168008e-06 9.66523748e-07
-1.53815319e-06]
[ -2.14579320e-08 5.95866729e-07 9.66523748e-07 4.53031826e-06
-1.61278260e-06]
[ -2.33234708e-07 -3.20550581e-07 -1.53815319e-06 -1.61278260e-06
1.74050730e-06]]

Retrieve the covariance matrix as a numpy N-D array.

Bugs

See the bugs pages on the Sherpa website for an up-to-date listing of known bugs.

See Also

confidence
conf, covariance, get_conf, get_int_proj, get_int_unc, get_proj, get_reg_proj, get_reg_unc, int_proj, int_unc, projection, reg_proj, reg_unc, set_conf_opt, set_covar_opt, set_proj_opt
contrib
get_chart_spectrum
data
get_areascal, get_arf, get_arf_plot, get_axes, get_backscal, get_bkg, get_bkg_plot, get_bkg_scale, get_coord, get_counts, get_data, get_data_plot, get_dep, get_dims, get_error, get_exposure, get_grouping, get_indep, get_quality, get_rmf, get_specresp, get_staterror, get_syserror
filtering
get_filter
fitting
calc_stat_info, get_fit, get_stat_info
info
get_default_id, list_stats
methods
get_draws, get_iter_method_name, get_iter_method_opt, get_method
modeling
get_model, get_model_component, get_model_component_image, get_model_component_plot, get_model_plot, get_num_par, get_order_plot, get_par, get_pileup_model, get_response, get_source, get_source_component_image, get_source_component_plot, image_source
plotting
get_split_plot
psfs
get_kernel, get_psf
statistics
get_chisqr_plot, get_delchi_plot, get_prior, get_sampler, get_stat
utilities
get_analysis, get_rate
visualization
get_ratio, get_resid, image_getregion

Last modified: December 2013
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