[Mpi-comments] MPI_Dims_create(..., ndims=0, ...) semantic ?

[William Gropp]

The standard doesn’t specify this, though I recall us discussing this and IIRC agreeing that ndims equal to zero was well-defined and not an error.  And there is nothing in the standard that suggests that it should be an error, just nothing that says it shouldn’t.

Bill

William Gropp
Acting Director and Chief Scientist, NCSA
Director, Parallel Computing Institute
Thomas M. Siebel Chair in Computer Science
University of Illinois Urbana-Champaign





On Nov 8, 2016, at 11:40 PM, Gilles Gouaillardet <gilles at rist.or.jp> wrote:

> Folks,
> 
> 
> Does the standard specifiy the behavior of MPI_Dims_create() when the ndims argument is zero ?
> 
> 
> the standard only says negative input values of dims[i] are erroneous, but does not say anything about ndims.
> 
> ndims is the number of Cartesian dimensions (integer), and though a negative number likely looks erroneous
> 
> to most of us, a zero value is incorrect from a mathematical point of view (and i wish i remembered that ...)
> 
> 
> Could someone tell me how a zero value should be interpreted ?
> 
> (e.g. valid/invalid/up to the implementor ?)
> 
> 
> FWIW, currently
> 
> in MPICH, this is a no-op.
> 
> In Open MPI, this is an error by default, but if parameter check is manually disabled, then this is a no-op too.
> 
> 
> Cheers,
> 
> 
> Gilles
> 
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