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Re: POLY_FIT 5.0: inaccurate results. use 4.0 if possible. [message #11526 is a reply to message #11308]

Mon, 30 March 1998 00:00

davidf
Messages: 2866
Registered: September 1996

Senior Member

Hi Folks,

Just to keep you up to date on this inaccurate POLY_FIT 5 saga,
I now hear from RSI technical support people that there is
a bug in the DOUBLE implementation. So, just to summarize.

Russ Welti reported that IDL 5 POLY_FIT gave different (and
apparently inaccurate) results compared to the IDL 5 POLY_FIT.
RSI reports that in the interest of execution speed, they
now make the calculation in single precision and to get the
same results as before we should set the DOUBLE keyword. (I
agree with Peter, by the way, that a SINGLE keyword would
have made more sense here.) But there is apparently still
a bug in the DOUBLE implementation, so the result is perhaps
even worse than doing it in single precision.

The work-around it to make the *data* a double precision
value before passing it to POLY_FIT. I'm told this will
be fixed before the final release of 5.1.

This reminds me of one of those times when I tried to do
something nice for my wife and it gets all fouled up and
she ends up not speaking to me for a week. :-(

Cheers,

David

-----------------------------------------------------------
David Fanning, Ph.D.
Fanning Software Consulting
E-Mail: davidf@dfanning.com
Phone: 970-221-0438
Coyote's Guide to IDL Programming: http://www.dfanning.com/

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[Message index]

		POLY_FIT 5.0: inaccurate results. use 4.0 if possible. By: Russ Welti (on mapper on Wed, 25 March 1998 00:00
		Re: POLY_FIT 5.0: inaccurate results. use 4.0 if possible. By: davidf on Mon, 30 March 1998 00:00
		Re: POLY_FIT 5.0: inaccurate results. use 4.0 if possible. By: pit on Mon, 30 March 1998 00:00

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