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Re: SVDFIT Problems
| Re: SVDFIT Problems [message #31936 is a reply to message #31931] |
Fri, 30 August 2002 10:08  |
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Paul Van Delst[1]
Messages: 1157
Registered: April 2002
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Senior Member |
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Bill wrote:
>
> In my occaisional attempts to use SVDFIT I have had problems in that it
> reports singular solutions when other fitting routines, e.g., REGRESS,
> have had not problems.
Deja vu! I was using the SVDFIT routine just yesterday to fit a second order polynomial. I kept
getting an error report for a singular value (even with /DOUBLE). Used POLY_FIT with no problems
(SVDFIT _was_ overkill for what I wanted to do.)
<snip>
> Unfortunately it appeas that the code currently relies on a simplified
> version of the Numerical Recipes routine SVDCMP, that does not return
> the singular value vector that Numerical Recipes uses to compute wmax. A
> rewrite to give SVDFIT the proper properties is more work than I am
> willing to put in at this time.
Thanks for taking the time to nut the problem out and report it here. It really pains me (just
having finished the yearly license renewal tooth-pulling process) that these sorts of things are
*still* found in incarnations of such well-worn linear algebra problems like SVD. I spent about half
a day trying to figure out what I was doing wrong until I tossed the lot and surfed over to
netlib.org for some fortran routines. I thought IDL was supposed to *save* time for this sort of
thing?
paulv
--
Paul van Delst
CIMSS @ NOAA/NCEP/EMC
Ph: (301)763-8000 x7274
Fax:(301)763-8545
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