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Last modified: December 2015

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

get_fit

Context: fitting

Synopsis

Return model fit information associated with a Sherpa data set.

Syntax

get_fit_plot([id])
get_fit_contour([id])
get_fit_results()

Description

  • id - the id of the data set to use; if not given, uses the default dataset id (id=1 by default, see "ahelp get_default_id").

get_fit_plot

The get_fit_plot() function returns the data and preferences defining the 'dataplot' and 'modelplot' which together produce the plot of a model fit to a dataset. Once a model is assigned to a data set, this command can be used to list the x, y, x error, and y error data arrays used in the data and model plots, in addition to the values for the x label, y label, units, title, and other plotting preferences (such as linestyle, linethickness, etc.). The information returned by get_fit_plot() may be stored in a variable, or printed to the screen, as shown in the examples section. The source data, the model assigned to the data, and the fit of the model to the data can be visualized with plot_data(), plot_model(), and plot_fit(), respectively.

get_fit_contour

The get_fit_contour() function returns the data and settings defining the 2-D 'datacontour' and 'modelcontour' plots which together produce the contour plot of the model fit to a 2-D data set. The fit contour plot can be visualized with the contour_fit() function. Once a 2-D model is assigned to a 2-D data set, this command can be used to list the x0, x1, and y data arrays used in the 2-D fit contour plot created with contour_fit(), in addition to the values for the x0 label, x1 label, title, and other plotting preferences. When called with no arguments, the fit contour associated with the default data set loaded in the Sherpa session will be returned. The information returned by get_fit_contour() may be stored in a variable, or printed to the screen, as shown in the examples section.

get_fit_results

The get_fit_results() function returns the results from the most recent fit, either source or background, in the Sherpa session. This function accepts no arguments.

Example 1

sherpa> print(get_fit_plot())
sherpa> print(get_fit_plot(2))
sherpa> print(get_fit_plot("src"))

When called with no arguments from within the print command, the data and preferences defining the plot of the model fit to the default data set loaded in the Sherpa session is returned. The user can also specify a data set ID to view the model fit for that data set.

sherpa> print(get_fit_plot(2))
dataplot   = simple.pi
x      = [ 0.0967  0.2336  0.292  ...,  9.4389  9.6506  9.8404]
y      = [ 0.0006  0.0002  0.0067 ...,  0.0005  0.0005  0.0006]
yerr   = [ 0.0014  0.0034  0.0077 ...,  0.001   0.0016  0.0012]
xerr   = [ 0.1825  0.0876  0.0292 ...,  0.2482  0.1752  0.2044]
xlabel = Energy (keV)
ylabel = Counts/sec/keV
title  = simple.pi
plot_prefs = {'errstyle': 'line', 'symbolfill': False, 'symbolstyle': 4, 'linestyle': 0, 'symbolsize': 3, 'yerrorbars': True}

modelplot  = Model
x      = [ 0.0967  0.2336  0.292  ...,  9.4389  9.6506  9.8404]
y      = [  9.8950e-05   1.0043e-03   4.1455e-03 ...,   1.3467e-05   1.0891e-05 8.4900e-06]
yerr   = None
xerr   = [ 0.1825  0.0876  0.0292 ...,  0.2482  0.1752  0.2044]
xlabel = Energy (keV)
ylabel = Counts/sec/keV
title  = Model
plot_prefs = {'symbolstyle': 0, 'linethickness': 3, 'linestyle': 1, 'linecolor': 'red'}

Example 2

sherpa> print(get_fit_contour())
sherpa> print(get_fit_contour(4))
sherpa> print(get_fit_contour("src"))

When called with no arguments from within the print command, the fit contour data associated with the default data set loaded in the Sherpa session is returned. The user can also specify a data set ID to view the data and settings defining the contour plot of a 2-D model fit to that data set.

sherpa> contour_fit(4)
sherpa> print(get_fit_contour(4))
datacontour = image.fits
x0     = [   1.    2.    3. ...,  259.  260.  261.]
x1     = [   1.    1.    1. ...,  216.  216.  216.]
y      = [ 0.  0.  0. ...,  0.  0.  0.]
xlabel = x0 (pixels)
ylabel = x1 (pixels)
title  = image.fits
levels = None
contour_prefs = {}
modelcontour = Model
x0     = [   1.    2.    3. ...,  259.  260.  261.]
x1     = [   1.    1.    1. ...,  216.  216.  216.]
y      = [  0.0000e+00  -1.1733e-05  -1.7269e-05 ...,  -4.2121e-07  -4.2984e-07  -4.3841e-07]
xlabel = x0 (pixels)
ylabel = x1 (pixels)
title  = Model
levels = None
contour_prefs = {'color': 'red', 'style': None, 'thickness': 3}

Example 3

sherpa> print(get_fit_results())

This function accepts no arguments, and will always return the fit results associated with the most recent fit in a Sherpa session.

sherpa> print(get_fit_results())
datasets   = (6,)
methodname = levmar
statname   = chi2gehrels
succeeded  = True
parnames   = ('p1.gamma', 'p1.ampl')
parvals    = (1.3876399720188146, 1.9303021425484831e-05)
covarerr   = None
statval    = 670.920704836
istatval   = 684.408012448
dstatval   = 13.4873076119
numpoints  = 1024
dof        = 1022
qval       = 1.0
rstat      = 0.656478184771
message    = both actual and predicted relative reductions in the sum of squares are at most ftol=1.19209e-07
nfev       = 13

The meaning of the fields

Label Meaning
succeeded boolean of fit success
parnames list of thawed parameter names
parvals list of thawed parameter values
statval statistic value
numpoints number of points on grid
dof degrees of freedom
qval probability Note: None for Cash
rstat reduced statistic value Note: None for Cash
message message from optimization method
nfev number of function evalutions

Bugs

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

See Also

confidence
get_conf, get_covar, get_int_proj, get_int_unc, get_proj, get_reg_proj, get_reg_unc
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_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 2015
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