Synopsis
Access the simulation results of the likelihood ratio test.
Syntax
get_pvalue_results()
Description
The get_pvalue_results() command returns the likelihood ratio test results computed by the plot_pvalue() command, comparing fits of the null model to fits of the alternative model using faked data with Poisson noise. The likelihood ratio based on the observed data is returned, along with the p-value, used to reject or accept the null model.
The following attributes are returned by get_pvalue_results():
- samples - parameter samples from all iterations, in the order of the parameter list (as many as samples as specified in the 'num' parameter of plot_pvalue() are returned; default is 500)
- stats - calculated fit statistics in all iterations (first column null, alt second)
- ratios - calculated likelihood ratios from all iterations
- null - fit statistic of null on real data
- alt - fit statistic of alt on real data
- lr - likelihood ratio on real data
- ppp - p-value
Examples
Example 1
sherpa> plot_pvalue(powlaw1d.p1, p1+gauss1d.g1) sherpa> print get_pvalue_results()
samples = [[ 8.5623e-01 5.6209e+03] [ 8.5391e-01 5.5819e+03] [ 8.5695e-01 5.7627e+03] ..., [ 8.6336e-01 5.9058e+03] [ 8.5459e-01 5.6061e+03] [ 8.3418e-01 4.9820e+03]] stats = [[ 466.1517 466.1517] [ 500.005 500.005 ] [ 474.0595 474.0595] ..., [ 424.5051 424.5051] [ 453.3375 453.3375] [ 463.3019 463.3019]] ratios = [-0. -0. -0. ..., -0. -0. -0.] null = 3958.4582610638136 alt = 3958.4582610638136 lr = -0.0 ppp = 0.054
Call the get_pvalue_results() command with no arguments to print to the screen the results of the likelihood ratio test performed by the plot_pvalue() command. View the array of ratios comparing fits to simulated data done with a simple (null) power-law model versus the more-complex (alternative) power-law plus Gaussian model, along with the likelihood ratio and p-value based on the observed data.
Example 2
lrt = get_pvalue_results()
Store the data returned by get_pvalue_results() to variable "lrt", in order to access and manipulate individual attributes within a script.
sherpa> res.ratios array([-0., -0., -0., ..., -0., -0., -0.]) sherpa> res.ppp 0.054 sherpa> res.stats array([[ 466.1517, 466.1517], [ 500.005 , 500.005 ], [ 474.0595, 474.0595], ..., [ 424.5051, 424.5051], [ 453.3375, 453.3375], [ 463.3019, 463.3019]]) sherpa> len(res.stats) 500 sherpa> res.stats[46] array([ 532.5428, 532.5428])
Bugs
See the bugs pages on the Sherpa website for an up-to-date listing of known bugs.
See Also
- contrib
- 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
- data
- get_arf_plot, get_bkg_plot
- info
- list_model_ids, show_bkg_model, show_bkg_source
- modeling
- 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
- plotting
- get_energy_flux_hist, get_lrt_plot, get_lrt_results, get_photon_flux_hist, get_pvalue_plot, 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
- psfs
- delete_psf, load_conv, plot_kernel
- saving
- save_delchi, save_resid
- statistics
- get_chisqr_plot, get_delchi_plot
- utilities
- calc_chisqr, calc_energy_flux, calc_model_sum, calc_photon_flux, calc_source_sum, calc_stat, eqwidth
- visualization
- contour_model, contour_ratio, contour_resid, get_ratio, get_resid