QFIT


Program QFIT computes the agreement factor for the fit of a  model  to
VLB-type data.  Both MERGE-formats 1 and 2 are accepted.

     To use the program, use the command QFIT.  The program  asks  for
an  input  data file, an input model file, and an output listing file.
The output table contains the agreement factors for each baseline, for
each  triangle,  for  all  the baselines together, for all the closure
phases together, and a total agreement factor.  Models with very  many
components  may  take  a few minutes of CPU time; small models require
only seconds.

     The agreement factor is defined as the square root of the reduced
chi-square  value  for the goodness-of-fit between the model and data.
Thus:

        Agreement factor = SQRT ( SUMSQR / N )

where
N = number of independent data points
SUMSQR = sum over the data of the square of the difference between the
        model  prediction  and the actual observation; each element in
        the sum is weighted by a factor equal to one over the observed
        error squared.

     The program keeps careful track  of  the  number  of  independent
triangles,  so  that the total agreement factor does not give too much
weight to the closure phases.

History:

Version 1.0:  1981 Jun 30 :  Richard S.  Simon.
Version 2.0:  1983 Jul 20 :  extend to include MERGE format Version  2
                            files  (D.   Meier); 1983 Aug 3 :  added W
                            to  version  2  files  1983   Oct   17   :
                            corrected bug in QMODAP when QQ=0.0; don't
                            bother doing VIS calc if ERR <= 0
Version 2.1:  1984 Mar  9 :   Fix  bugs  in  visibility  calc  when  C
                            TYPE.GT.1:  QGETMOD, QMODAP
Version 3.0:  1988 Apr 19 :  changes for Convex [TJP].
Version 3.1:  1988 Jul 14 :  correct dimension error for array CSUM.
Version 3.2:  1989 Mar  6 :  correct bug:  compute all visibilities in
                            case closure phases need them [TJP].
Version 3.3:  1989  Jun  21  :   correct  bug  in  TRIANGLE.   Program
                            computed   closure  phase  incorrectly  if
                            baselines not  in  canonical  order.   New
                            algorithm    for    finding    number   of
                            independent closure phases [TJP].
Version 3.4:  1990 Nov 5 :  another algorithm for  finding  number  of
                            independent closure phases [TJP].