HEASARC Staff Scientist Position - Applications are now being accepted for a Staff Scientist with significant experience and interest in the technical aspects of astrophysics research, to work in the High Energy Astrophysics Science Archive Research Center (HEASARC) at NASA Goddard Space Flight Center (GSFC) in Greenbelt, MD. Refer to the AAS Job register for full details.

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ftest

calculate the F-statistic from two chi-square values

Calculate the F-statistic and its probability given new and old values of $\chi^2$and number of degrees of freedom (DOF).

Syntax: ftest chisq2 dof2 chisq1 dof1

The new $\chi^2$and DOF, chisq2 and dof2, should come from adding an extra model component to (or thawing a frozen parameter of) the model which gave chisq1 and dof1. If the F-test probability is low then it is reasonable to add the extra model component. WARNING : it is not correct to use the F-test statistic to test for the presence of a line (see Protassov et al 2002, ApJ 571, 545). WARNING: this command can only be used if the extra model component is additive, this does not give the correct result if the component is multiplicative (see Orlandini et al. 2012, ApJ 748, 86).

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Last modified: Friday, 23-Aug-2024 13:20:40 EDT

HEASARC Staff Scientist Position - Applications are now being accepted for a Staff Scientist with significant experience and interest in the technical aspects of astrophysics research, to work in the High Energy Astrophysics Science Archive Research Center (HEASARC) at NASA Goddard Space Flight Center (GSFC) in Greenbelt, MD. Refer to the AAS Job register for full details.