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.TH CHIFIT 3M
.SH NAME
chifit
.SH DESCRIPTION
subroutine chifit.f
source
Bevington, pages 228-231.
purpose
make least-squares fit to a non-linear function
with a parabolic expansion of chi square
usage
call chifit (x, y, sigmay, npts, nterms, mode, a, deltaa,
sigmaa, yfit, chisqr)
description of parameters
x - array of data points for independent variable
y - array of data points for dependent variable
sigmay - array of standard deviations for y data points
npts - number of pairs of data points
nterms - number of parameters
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)
a - array of parameters
deltaa - array of increments for parameters a
sigmaa - array of standard deviations for parameters a
yfit - array of calculated values of y
chisqr - reduced chi square for fit
subroutines and function subprograms required
functn (x, i, a)
evaluates the fitting function for the ith term
fchisq (y, sigmay, npts, nfree, mode, yfit)
evaluates reduced chi squared for fit to data
matinv (array, nterms, det)
inverts symmetric two-dimension matrix of degree nterms
and calculates its determinant
comments
valid for nterms up to 10
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