Re: [AMBER-Developers] Fortran experts, a word of advice please

From: <>
Date: Wed, 25 Jul 2012 04:04:11 -0400 (EDT)


>> xmolnu 40.3614616595491
>> -xmol -40.3635833689616
> First: are you sure that x(1,i), xmolnu, and xmol are exactly the same on
> V0 and V1?

yes, at least to the degree that a write (6,*) prints them. The numbers
above have 15 digits, I believe that is the expected amount for our _REAL_

> Second: try adding -fltconsistency and/or -fp-model precise to the flags
> for

Compiling with additional switches solves the problem indeed, at a cost:

-fltconsistency: 30% runtime increase
-O0 instead of -O3 -xHost 100% runtime increase
-fp-model precise 10% runtime increase

(runtimes measured on my simple 10 md-step test case.)

So it looks like '-fp-model precise' works best and should be added to the
compiler directives. Is there a way to tell 'make' that only softcore.F90
should need this flag? In config.h, it is set for the whole compile.

Is there a similar compiler directive for the Portland group compilers
which appear to show the same behaviour (I couldnt verify that, since I
dont have those)

Thanks Dave,


Dr. Thomas Steinbrecher
formerly at the
BioMaps Institute
Rutgers University
610 Taylor Rd.
Piscataway, NJ 08854

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Received on Wed Jul 25 2012 - 01:30:04 PDT
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