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Re: crazy loops [message #29359 is a reply to message #29354]

Wed, 13 February 2002 05:35

David Fanning
Messages: 11724
Registered: August 2001

Senior Member

M Carmen (mcgonzal@uv.es) writes:

> I have a question related with loops......can someone teel me why
>
> if i do a loop that goes to a maximum of 0.6:
> for r=0.0, 0.6, 0.1 do begin & print, r & endfor
>
> I get:
> 0.000000
> 0.100000
> [........]
> 0.500000
> 0.600000
>
> and if now i change the maximum value of the range to 0.7:
> for r=0.0, 0.7, 0.1 do begin & print, r & endfor
>
> I get:
> 0.000000
> 0.100000
> [........]
> 0.500000
> 0.600000
>
> EXACTLY THE SAME!!!

Well, the short answer is "Because of the way computers
represent floating point numbers." There have been numerous
posts on this topic in the past. You might try searching
the Google archives for "Set Precision", for example. The
bottom line, however, is that it is not a good idea to use
floating point values as counters, since you can't rely on
their exact value. This has nothing to do with IDL. It is
entirely related to how computers work.

Cheers,

David

--
David W. Fanning, Ph.D.
Fanning Software Consulting
Phone: 970-221-0438, E-mail: david@dfanning.com
Coyote's Guide to IDL Programming: http://www.dfanning.com/
Toll-Free IDL Book Orders: 1-888-461-0155

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[Message index]

		Re: crazy loops By: Andre Kyme on Wed, 13 February 2002 14:11
		Re: crazy loops By: Robert Stockwell on Wed, 13 February 2002 09:14
		Re: crazy loops By: Craig Markwardt on Wed, 13 February 2002 06:04
		Re: crazy loops By: David Fanning on Wed, 13 February 2002 05:35

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