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Subject: Re: [OMPI users] MPI_Cart_sub periods
From: Jeff Squyres (jsquyres_at_[hidden])
Date: 2012-09-06 10:23:04


John --

This cartesian stuff always makes my head hurt. :-)

You seem to have hit on a bona-fide bug. I have fixed the issue in our SVN trunk and will get the fixed moved over to the v1.6 and v1.7 branches.

Thanks for the report!

On Aug 29, 2012, at 5:32 AM, Craske, John wrote:

> Hello,
>
> We are partitioning a two-dimensional Cartesian communicator into
> two one-dimensional subgroups. In this situation we have found
> that both one-dimensional communicators inherit the period
> logical of the first dimension of the original two-dimensional
> communicator when using Open MPI. Using MPICH each
> one-dimensional communicator inherits the period corresponding to
> the dimensions specified in REMAIN_DIMS, as expected. Could this
> be a bug, or are we making a mistake? The relevant calls we make in a
> Fortran code are
>
> CALL MPI_CART_CREATE(MPI_COMM_WORLD, 2, (/ NDIMX, NDIMY /), (/ .True., .False. /), .TRUE.,
> COMM_CART_2D, IERROR)
>
> CALL MPI_CART_SUB(COMM_CART_2D, (/ .True., .False. /), COMM_CART_X, IERROR)
> CALL MPI_CART_SUB(COMM_CART_2D, (/ .False., .True. /), COMM_CART_Y, IERROR)
>
> Following these requests,
>
> CALL MPI_CART_GET(COMM_CART_X, MAXDIM_X, DIMS_X, PERIODS_X, COORDS_X, IERROR)
> CALL MPI_CART_GET(COMM_CART_Y, MAXDIM_Y, DIMS_Y, PERIODS_Y, COORDS_Y, IERROR)
>
> will result in
>
> PERIODS_X = T
> PERIODS_Y = T
>
> If, on the other hand we define the two-dimensional communicator
> using PERIODS = (/ .False., .True. /), we find
>
> PERIODS_X = F
> PERIODS_Y = F
>
> Your advice on the matter would be greatly appreciated.
>
> Regards,
>
> John.
>
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-- 
Jeff Squyres
jsquyres_at_[hidden]
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