[Wien] Re: Single/Precision issues

[L. D. Marks]

On the topic of precision, can I suggest adding -fpconstant to the
suggested ifort options. To quote from the man page:

"Tells the compiler to extend the precision to double precision for
single-precision constants assigned to double-precision variables"

This may catch some of the precision issues. (I've not seen problems,
although I have not used everything in Wien.)

It might also be good to suggest that users use the appropriate -ax<p>
flag for their CPU since this turns on some fairly useful (10-15% faster)
optimizations particularly for some of the newer CPUs.

Last, I would suggest care with ifort 8.0. Intel calls ifort 8.1 a
"maintenance release" and does not go into any details. My observation is
that 8.1 produces executables about 5% slower than 8.0, which suggests
that 8.0 does some optimizations cutting corners which it is not supposed
to.

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Laurence Marks
Department of Materials Science and Engineering
MSE Rm 2036 Cook Hall
2220 N Campus Drive
Northwestern University
Evanston, IL 60201, USA
Tel: (847) 491-3996 Fax: (847) 491-7820
email: L - marks @ northwestern . edu
http://www.numis.northwestern.edu
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