Last modified: December 2015

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AHELP for CIAO 4.12 Sherpa v1


Context: confidence


Create a confidence plot of fit statistic vs. parameter value.


int_proj(par, id=None, otherids=None, replot=False, fast=True,
min=None, max=None, nloop=20, delv=None, fac=1, log=False,
numcores=None, overplot=False)


The int_proj command creates a confidence plot of fit statistic as a function of parameter value, with dashed lines indicating the best fit statistic and best fit parameter value. The parameter value is varied on the computed grid until the fit statistic is increased by delta_S, which is a function of sigma (e.g., delta_S = 1 if the statistic is chi-square and fac = 1).

int_proj differs from int_unc ("ahelp int_unc") in that all other thawed parameters are allowed to float to new best-fit values, instead of being fixed to the initial best-fit values. This makes the plot created by int_proj a more accurate rendering of the projected shape of statistical hypersurface, but the computation is slower.

The computationally intensive projection function is parallelized to make use of multi-core systems (i.e., laptops or desktops with 2 or 4 cores) to provide significant improvements in efficiency compared to previous releases of Sherpa; the 'numcores' argument may be used to specify how the cores should be used when projection is run.

The calculated values, such as the grid min and max, can be retrieved with get_int_proj ("ahelp get_int_proj").

The plot is displayed in a ChIPS plotting window. If there is no plotting window open, one is created. If a plotting window exists, the overplot parameter value determines whether the new plot is overlaid on any existing plots in the window or if the window is cleared before the plot is drawn.

ChIPS commands may be used within Sherpa to modify plot characteristics and create hardcopies; refer to the ChIPS website for information.


Example 1

sherpa> int_proj(p1.gamma, id=1)

Run int_proj on the parameter p1.gamma from dataset 1.

Example 2

sherpa> int_proj(const.c0, id="bkg")

Run int_proj for the parameter const.c0 in the dataset "bkg".

Example 3

sherpa> int_proj(p1.gamma, 1, [2,3])

int_proj is run for parameter p1.gamma for datasets 1, 2, and 3.

Example 4

sherpa> int_proj(p1.gamma, min=2.0, max=2.5)

Manually set the grid limits to 2.0 (lower bound) and 2.5 (upper bound) before running int_proj for p1.gamma.

Example 5

sherpa> int_proj(src1.c2, log=True)

Use a log grid when running int_proj on the parameter src1.c2.

Example 6

sherpa> int_proj(p1.gamma, overplot=True)

Run int_proj on p1.gamma, overlaying the results on any existing plot.


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

See Also

conf, covariance, get_conf, get_covar, get_int_proj, get_int_unc, get_proj, get_reg_proj, get_reg_unc, int_unc, projection, reg_proj, reg_unc, set_conf_opt, set_covar_opt, set_proj_opt