---
name: "fchisq"
section: "3m"
platform: "linux"
package: "iraf"
version: "2.11.3-2"
release: "Debian 3.0 (Woody)"
platforms: ["linux"]
url: "https://new.carta.tech/fchisq"
---

# fchisq(3m)

## NAME

fchisq

## DESCRIPTION

function fchisq.f

source\
   Bevington, page 194.

purpose\
   evaluate reduced chi square for fit of data \
     fchisq = sum ((y-yfit)\*\*2 / sigma\*\*2) / nfree

usage \
   result = fchisq (y, sigmay, npts, nfree, mode, yfit)

description of parameters\
   y      - array of data points\
   sigmay - array of standard deviations for data points\
   npts   - number of data points\
   nfree  - number of degrees of freedom\
   mode   - determines method of weighting least-squares fit\
            \+1 (instrumental) weight(i) = 1./sigmay(i)\*\*2\
             0 (no weighting) weight(i) = 1.\
            \-1 (statistical)  weight(i) = 1./y(i)\
   yfit   - array of calculated values of y

subroutines and function subprograms required \
   none