Re: gcc/gsl

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How different are the values?      How many significant figures match?  0? 5?

On Wed, Nov 13, 2024 at 12:33 PM Patrick Dupre via users
<users@xxxxxxxxxxxxxxxxxxxxxxx> wrote:
>
> Hello,
>
> I am not sure this issue is entirely relevant on this mailing list.
> Maybe you could redirect me.
>
> The same application (relatively heavy code), provides different values when it
> is run and compiled on 2 different machines.
> Both F40 (last update)
> gcc (GCC) 14.2.1 20240912 (Red Hat 14.2.1-3)
> One
> Intel(R) Core(TM) i5-7400 CPU @ 3.00GHz
> The other one
> Intel(R) Core(TM) i7-8700 CPU @ 3.20GHz
> Actually, this happens when I use the gsl library.
> gsl-devel-2.7.1-8.fc40.x86_64
> for integration (gsl_integration_cquad).
> Before integration, the values are strictly identical.
> The same Makefile is used.
> Now, if I copy the code generated by the machine A on machine B,
> I get the same results as it had been run on machine A.
> The size of both codes are slightly different.
> I conclude that the issue is due to the compiler.
> Indeed, the difference in the generated values seems pretty constant,
> i.e., it seems proportional to the value itself: of the order 2.7e-8 (relative difference)
> i.e. a lot higher than the accuracy of the machine: < 1e-35.
>
> Which one is the good one?
> Why this behavior?
> Can I solve the issue?
>
> Thank for any help.
>
> ===========================================================================
>  Patrick DUPRÉ                                 | | email: pdupre@xxxxxxx
> ===========================================================================
>
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