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

# regres(3m)

## NAME

regres

## DESCRIPTION

subroutine regres.f

source\
   Bevington, pages 172-175.

purpose\
   make mulitple linear regression fit to data with specified\
     function which is linear in coefficients

usage\
   call regres (x, y, sigmay, npts, nterms, m, mode, yfit,\
     a0, a, sigma0, sigmaa, r, rmul, chisqr, ftest)

description of parameters\
   x      - array of points for independent variable\
   y      - array of points for dependent variable\
   sigmay - array of standard deviations for y data points\
   npts   - number of pairs of data points\
   nterms - number of coefficients\
   m      - array of inclusion/rejection criteria for fctn\
   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\
   a0     - constant term\
   a      - array of coefficients\
   sigma0 - standard deviation of a0\
   sigmaa - array of standard deviations for coefficients\
   r      - array of linear correlation coefficients\
   rmul   - multiple linear correlation coefficient\
   chisqr - reduced chi square for fit\
   ftest  - value of f for test of fit

subroutines and function subprograms required\
   fctn (x, i, j, m)\
     evaluates function for the jth term and the ith data\
       point using array m to specify terms in function\
   matinv (array, nterms, det)\
     inverts symmetric two-dimension matrix of degree nterms\
       and calculates its determinant

comments\
   valid for npts up to 100 and nterms up to 10\
   one source line modified - sigmaa substituted for sigmaag