Last modified: December 2013

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AHELP for CIAO 4.12 Sherpa v1


Context: plotting


Access a histogram plot of likelihood ratio test results.


get_lrt_plot([null_model=None, alt_model=None, conv_model=None, id=1,
otherids=(), num=500, bins=25, numcores=None, recalc=False])


Access the data arrays and preferences defining the histogram plot produced by the plot_lrt() function, a histogram of the likelihood ratios comparing fits of the null model to fits of the alternative model using faked data with Poisson noise. Data returned includes the likelihood ratio computed using the observed data, and the p-value, used to reject or accept the null model.


The get_lrt_plot() function returns the following attributes:


Example 1

sherpa> plot_lrt(powlaw1d.p1, bpowlaw1d.bp1)
sherpa> print get_lrt_plot()
ratios = [ 0.303   2.3149  0.5895 ..., -9.5852 -2.3156 -4.92  ]
lr = 12566.880545
xlo    = [-88.6406 -85.0598 -81.4791 ...,  -6.2833  -2.7026   0.8782]
xhi    = [-85.0598 -81.4791 -77.8983 ...,  -2.7026   0.8782   4.4589]
y      = [ 0.002  0.     0.    ...,  0.114  0.672  0.01 ]
xlabel = Likelihood Ratio
ylabel = Frequency
title  = Likelihood Ratio Distribution
histo_prefs = {'linethickness': None, 'symbolcolor': None, 'symbolfill': None, 'xlog': False, 'ylog': False, 'symbolangle': None, 'errthickness': None, 'fillcolor': None, 'linecolor': None, 'errstyle': None, 'linestyle': 1, 'symbolstyle': 0, 'errcolor': None, 'fillstyle': None, 'fillopacity': None, 'yerrorbars': False, 'symbolsize': None}

Call the get_lrt_plot() command with no arguments to print to the screen the data arrays and preferences defining a histogram of likelihood ratios calculated using the plot_lrt() command. View the arrays of ratios comparing fits to simulated data done with a simple (null) power-law model versus the more-complex (alternative) broken power-law model.

Example 2

sherpa> plot_lrt(p1, p1+g1)
sherpa> my_lrt_plot = get_lrt_plot()
sherpa> my_lrt_plot.ratios
array([ 0.303 ,  2.3149,  0.5895, ..., -9.5852, -2.3156, -4.92  ])

Store the data arrays and plot preferences returned by get_lrt_plot() to variable "my_lrt_plot", in order to access and manipulate individual attributes within a script.


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

See Also

get_data_prof, get_data_prof_prefs, get_delchi_prof, get_delchi_prof_prefs, get_fit_prof, get_model_prof, get_model_prof_prefs, get_resid_prof, get_resid_prof_prefs, get_source_prof, get_source_prof_prefs, plot_chart_spectrum, plot_marx_spectrum, prof_data, prof_delchi, prof_fit, prof_fit_delchi, prof_fit_resid, prof_model, prof_resid, prof_source
get_arf_plot, get_bkg_plot
list_model_ids, show_bkg_model, show_bkg_source
add_model, add_user_pars, clean, create_model_component, delete_bkg_model, delete_model, delete_model_component, get_model, get_model_autoassign_func, 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_source, get_source_component_image, get_source_component_plot, image_model, image_model_component, image_source, image_source_component, integrate, link, load_table_model, load_template_model, load_user_model, normal_sample, reset, save_model, save_source, set_bkg_model, set_full_model, set_model_autoassign_func, set_pileup_model, set_source, set_xsabund, set_xscosmo, set_xsxsect, set_xsxset, t_sample, uniform_sample
get_energy_flux_hist, get_lrt_results, get_photon_flux_hist, get_pvalue_plot, get_pvalue_results, get_split_plot, plot, plot_arf, plot_bkg, plot_cdf, plot_chisqr, plot_data, plot_delchi, plot_energy_flux, plot_fit, plot_model, plot_model_component, plot_order, plot_pdf, plot_photon_flux, plot_pvalue, plot_ratio, plot_resid, plot_scatter, plot_source, plot_source_component, plot_trace, set_xlinear, set_xlog, set_ylinear, set_ylog
delete_psf, load_conv, plot_kernel
save_delchi, save_resid
get_chisqr_plot, get_delchi_plot
calc_chisqr, calc_energy_flux, calc_model_sum, calc_photon_flux, calc_source_sum, calc_stat, eqwidth
contour_model, contour_ratio, contour_resid, get_ratio, get_resid