Re: machar and ifort


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Posted by Valera on June 11, 2007 at 12:36:52:

In Reply to: machar and ifort posted by Michal Tarana on June 09, 2007 at 17:40:05:

Hi Michal,
if you have a look at src/util/machar.f you will find out that for some platforms these numbers are hardcoded, but for others - are computed..

And I can give a simple explanation - why (sometimes) it is impossible to use "standard" way of computing machine dependent constants.
Let's look at the simple statement:
IF(eps+1.gt.1)
A very 'smart' compiler (with -O2) can simplify the condition to
IF(eps.gt.0)

So. The only way to avoid this problem is to hardcode these constants..

I also believe that the problem you reported in another message is related to the fact that on AMD64 machine dependent constants are computed (and wrong), so you have a convergence problem.



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