[gmx-users] odd replica excahnge

[Mark Abraham]

On Mon, Dec 1, 2014 at 4:39 PM, leila salimi <leilasalimi at gmail.com> wrote:

> Dear gromacs users,
>
> I have tried different replica exchanges for my system, like 12, 14. I
> found that with 15 replica, I can get 30-40 % ratio of exchanges between
> replicas!
>

I don't understand. Below, you failed to run with 15 replicas.


> When I sumbitted a simulation with 15 replicas, I did not get any result
> and I got this error :
>
> ERROR: 0031-725  Failed to exec program mdrun_mpi_d; errno = 2
> ERROR: 0031-619  execvp error: No such file or directory
> ERROR: 0031-725  Failed to exec program mdrun_mpi_d; errno = 2
> ERROR: 0031-619  execvp error: No such file or directory
> ERROR: 0031-725  Failed to exec program mdrun_mpi_d; errno = 2
> ERROR: 0031-619  execvp error: No such file or directory
>
> I don't have any idea about this error!! It might be beacuse of odd
> replicas?!


No, as you will see if you try to run with 16 replicas. You have not set up
your environment so that mdrun is in the path / whatever.


>   If yes, I don't know the point that why the number of replicas
> should be even.
>

It doesn't have to be even. It's just usually efficient to do so because
parallel computers sometimes require the use of resources in multiples of 2.

Mark


>
> Kind Regards,
> Leila
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