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CUDA-x86.

Different answers

 
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cyclone6



Joined: 06 Aug 2004
Posts: 1

PostPosted: Thu Sep 16, 2004 7:14 am    Post subject: Different answers Reply with quote

I am trying to compile and execute the CALMET/CALPUFF modeling system on a linux box, but cannot seem to get the same results I do within windows. I have read some of the tips about precision, and tried most of them, to no avail. Here in a nutshell is what I've gotten:

1) AMD 2600+ - Windows 2000 - compiled with Compaq Visual Fortran - gives a result of 78.320.

2) Same machine as above - compiled with PGF 5.2-2 - gives a result of 78.320.

3) Intel P3 550 mHz - RedHat 8.0 - compiled with PGF 5.2-2, pgf90 -tp p6 -pc 80 - gives a result of 77.822.

I have tried many different switch combinations, all to no avail. It just wants to give me 77.822. Any ideas?

Thanks...
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mkcolg



Joined: 30 Jun 2004
Posts: 5815
Location: The Portland Group Inc.

PostPosted: Thu Sep 16, 2004 8:40 am    Post subject: x87 vs SSE Reply with quote

This is most likely an issue between 80-bit x87 floating point representation and 64-bit SSE floating point representation. Optimizing compilers will try and keep values in registers so using the x87 will accumulate 80-bit values. With small values and/or many calculations, these extra bits add-up leading to different answers than the same calculation in 64-bits.

What happens when you use "-Kieee -pc 64" on the P3?

We actually have an FAQ about this issue at http://www.pgroup.com/support/execute.htm#precision

- Mat
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sreid



Joined: 15 Feb 2005
Posts: 1

PostPosted: Tue Feb 15, 2005 6:45 pm    Post subject: compiling CALMET Reply with quote

I came across this post because I am also having problems compiling CALMET on a linux box with a PG compiler. Specifically, I'm getting a lot of "multiple definition references.

I know the code must be altered for different compilers, so maybe I'm not making the right changes for PG.

Any ideas or guidance would be greatly appreciated!
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mkcolg



Joined: 30 Jun 2004
Posts: 5815
Location: The Portland Group Inc.

PostPosted: Thu Feb 17, 2005 12:32 pm    Post subject: Reply with quote

Hello sreid,

Is this code freely available and if so, do you know where I can download it? I searched the web and could only find precompiled executables. A ftp site at the University of Edinburgh looked promising but I was unable to connect.

I'd like to help, but without the code or more information about the exact error, I'd only be guessing as to the cause.

Thanks,
Mat
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