| Re: format questions [message #51634] |
Fri, 01 December 2006 11:34 |
Foldy Lajos
Messages: 268
Registered: October 2001
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Senior Member |
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On Fri, 1 Dec 2006, lee wrote:
> Thank you very much for your quick response, David. Even I added
> format, the number changed a little bit (see below). How to get it
> exactly right? Your website is so helpful and thank you very much!
>
>> print, mx, FORMAT='(D20.10)'
> 598594.3750000000
> (the original number is 598594.35000000)
>
mx should be double, use mx=0.0d (instead of mx=0.0).
regards,
lajos
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| Re: format questions [message #51636 is a reply to message #51634] |
Fri, 01 December 2006 11:30  |
David Fanning
Messages: 11724
Registered: August 2001
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Senior Member |
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lee writes:
> Thank you very much for your quick response, David. Even I added
> format, the number changed a little bit (see below). How to get it
> exactly right? Your website is so helpful and thank you very much!
>
>> print, mx, FORMAT='(D20.10)'
> 598594.3750000000
> (the original number is 598594.35000000)
Well, I think maybe you want to read that article one more
time, a little more carefully than you did the last time!
MX is a float in your code. The best precision you can
expect is seven significant figures. These two numbers
are identical to that level of precision. :-)
Cheers,
David
--
David Fanning, Ph.D.
Fanning Software Consulting, Inc.
Coyote's Guide to IDL Programming: http://www.dfanning.com/
Sepore ma de ni thui. ("Perhaps thou speakest truth.")
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| Re: format questions [message #51637 is a reply to message #51636] |
Fri, 01 December 2006 11:25 |
lee
Messages: 3
Registered: February 1993
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Junior Member |
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Thank you very much for your quick response, David. Even I added
format, the number changed a little bit (see below). How to get it
exactly right? Your website is so helpful and thank you very much!
> print, mx, FORMAT='(D20.10)'
598594.3750000000
(the original number is 598594.35000000)
David Fanning wrote:
> lee writes:
>
>> ## Question : print out is different from the original file!!!!!!,
>> why?????
>> IDL> print, mx
>> 598594.
>> IDL> print, double(mx)
>> 598594.38
>> IDL> print, double(my)
>> 6738650.0
>
> Because you are not using a FORMAT that delivers enough
> accuracy. See the following article, about in the middle:
>
> http://www.dfanning.com/math_tips/sky_is_falling.html
>
> Something like:
>
> IDL> Print, mx, FORMAT='(D20.10)'
>
> Cheers,
>
> David
> --
> David Fanning, Ph.D.
> Fanning Software Consulting, Inc.
> Coyote's Guide to IDL Programming: http://www.dfanning.com/
> Sepore ma de ni thui. ("Perhaps thou speakest truth.")
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| Re: format questions [message #51641 is a reply to message #51637] |
Fri, 01 December 2006 11:10 |
David Fanning
Messages: 11724
Registered: August 2001
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Senior Member |
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lee writes:
> ## Question : print out is different from the original file!!!!!!,
> why?????
> IDL> print, mx
> 598594.
> IDL> print, double(mx)
> 598594.38
> IDL> print, double(my)
> 6738650.0
Because you are not using a FORMAT that delivers enough
accuracy. See the following article, about in the middle:
http://www.dfanning.com/math_tips/sky_is_falling.html
Something like:
IDL> Print, mx, FORMAT='(D20.10)'
Cheers,
David
--
David Fanning, Ph.D.
Fanning Software Consulting, Inc.
Coyote's Guide to IDL Programming: http://www.dfanning.com/
Sepore ma de ni thui. ("Perhaps thou speakest truth.")
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