November 2016 - mpi-comments - mailman3.cels.anl.gov

Re: [Mpi-comments] MPI_Dims_create(..., ndims=0, ...) semantic ?
by William Gropp 11 Nov '16

11 Nov '16

I’ll add something, but I disagree that this is a change - the standard is implicitly quite clear - ndim can be an integer, and 0 is an integer. 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 10, 2016, at 2:52 AM, Rolf Rabenseifner <rabenseifner(a)hlrs.de> wrote: > Yes I agree: Bill's solution is better, but it requires that the > MPI libraries may Need to be fixed, because then, ndimm==0 && nnodes==1 > is no error. > Currently, it is undefined, i.e., a MPI library may handle it > as an erronous input and may call the error handler. > I.e., this solution would require a change log entry that > all MPI library developers check there code. > > Proposal: I would add after the Example 7.1 on MPI-3.1 page 293 line 42 > > If ndims is zero, then nnodes must be one, and the argument > dims will be ignored, i.e., there will be no output. > > Changelog in "Changes in MPI-4.0": > > Section 7.5.2 on page 792. > MPI_DIMS_CREATE was extended to additionally allow a zero-dimensional > Cartesian topology, i.e., input ndims==0 together with nnodes==1. > > Bill, please can you provide the ticket/issue/... with probably > better wording ... > > Rolf > > ----- Original Message ----- >> From: "wgropp" <wgropp(a)illinois.edu> >> To: "Comments on the MPI Standard" <mpi-comments(a)lists.mpi-forum.org> >> Sent: Wednesday, November 9, 2016 7:04:44 PM >> Subject: Re: [Mpi-comments] MPI_Dims_create(..., ndims=0, ...) semantic ? > >> I agree with the analysis of the output but disagree with the conclusion - to >> make the behavior consistent with that of MPI_Cart_create, ndim == 0 should be >> permitted (with nnodes == 1) but there is, as noted, no output other than a >> return value / error value set of MPI_SUCCESS. Otherwise the use of >> MPI_Dims_create with MPI_Cart_create in the general case looks like >> >> if (ndim > 0) MPI_Dims_create(…) >> MPI_Cart_create(…) >> >> while the intent of the changes for MPI_Cart_create was to allow >> >> MPI_Dims_create(…) >> MPI_Cart_create(…) >> >> even if ndim == 0. >> >> 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 9, 2016, at 9:17 AM, Rolf Rabenseifner < [ mailto:[email protected] | >> rabenseifner(a)hlrs.de ] > wrote: >> >> >> >> We added all that the MPI_CART_... routines work fine with ndims==0. >> >> We oversaw that MPI_DIMS_CREATE is also a candidate for ndims==0. >> >> Reading the standard, I would say that MPI_DIMS_CREATE >> - with ndims==0 can never have any output, because >> the ndims Array has no element, >> - with ndims==0 and nnodes != 1 is erronous >> because a zero-dim-cart-topology has alwas exactly one node >> (and erronous implies always undefined behavior, >> i.e., the MPI library may catch or ignore this error), >> - with ndims==0 and nnodes == 1 would be okay but would not >> produce any output (because ndims has no entries), >> - but compared to the other CART routines where ndims==0 >> behaviour is always explicitely specified, I would conclude >> that MPI_DIMS_CREATE with ndims==0 has always undefined >> behavior, i.e., that also ndims==0 and nnodes == 1 may be >> treated by the MPI library as erronous. >> >> Therefore, I would recommend to clarify the standard by >> defining ndims of MPI_DIMS_CREATE as "positive integer" >> instead of only "integer". >> >> Rolf >> >> ----- Original Message ----- >> >> >> From: "wgropp" < [ mailto:[email protected] | wgropp(a)illinois.edu ] > >> To: "Comments on the MPI Standard" < [ mailto:[email protected] | >> mpi-comments(a)lists.mpi-forum.org ] > >> Sent: Wednesday, November 9, 2016 3:18:10 PM >> Subject: Re: [Mpi-comments] MPI_Dims_create(..., ndims=0, ...) semantic ? >> >> >> >> 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 < [ [ mailto:[email protected] >> | mailto:[email protected] ] | >> [ mailto:[email protected] | gilles(a)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 >> >> _______________________________________________ >> mpi-comments mailing list >> [ [ mailto:[email protected] | >> mailto:[email protected] ] | [ >> mailto:[email protected] | mpi-comments(a)lists.mpi-forum.org ] ] >> [ https://lists.mpi-forum.org/mailman/listinfo/mpi-comments | >> https://lists.mpi-forum.org/mailman/listinfo/mpi-comments ] >> >> >> _______________________________________________ >> mpi-comments mailing list >> mpi-comments(a)lists.mpi-forum.org >> https://lists.mpi-forum.org/mailman/listinfo/mpi-comments >> >> -- >> Dr. Rolf Rabenseifner . . . . . . . . . .. email [ mailto:[email protected] | >> rabenseifner(a)hlrs.de ] >> High Performance Computing Center (HLRS) . phone ++49(0)711/685-65530 >> University of Stuttgart . . . . . . . . .. fax ++49(0)711 / 685-65832 >> Head of Dpmt Parallel Computing . . . [ http://www.hlrs.de/people/rabenseifner | >> www.hlrs.de/people/rabenseifner ] >> Nobelstr. 19, D-70550 Stuttgart, Germany . . . . (Office: Room 1.307) >> _______________________________________________ >> mpi-comments mailing list >> [ mailto:[email protected] | mpi-comments(a)lists.mpi-forum.org ] >> https://lists.mpi-forum.org/mailman/listinfo/mpi-comments >> >> >> _______________________________________________ >> mpi-comments mailing list >> mpi-comments(a)lists.mpi-forum.org >> https://lists.mpi-forum.org/mailman/listinfo/mpi-comments > > -- > Dr. Rolf Rabenseifner . . . . . . . . . .. email rabenseifner(a)hlrs.de > High Performance Computing Center (HLRS) . phone ++49(0)711/685-65530 > University of Stuttgart . . . . . . . . .. fax ++49(0)711 / 685-65832 > Head of Dpmt Parallel Computing . . . www.hlrs.de/people/rabenseifner > Nobelstr. 19, D-70550 Stuttgart, Germany . . . . (Office: Room 1.307) > _______________________________________________ > mpi-comments mailing list > mpi-comments(a)lists.mpi-forum.org > https://lists.mpi-forum.org/mailman/listinfo/mpi-comments _______________________________________________ mpi-comments mailing list mpi-comments(a)lists.mpi-forum.org https://lists.mpi-forum.org/mailman/listinfo/mpi-comments

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Re: [Mpi-comments] MPI_Dims_create(..., ndims=0, ...) semantic ?
by Rolf Rabenseifner 10 Nov '16

10 Nov '16

Yes I agree: Bill's solution is better, but it requires that the MPI libraries may Need to be fixed, because then, ndimm==0 && nnodes==1 is no error. Currently, it is undefined, i.e., a MPI library may handle it as an erronous input and may call the error handler. I.e., this solution would require a change log entry that all MPI library developers check there code. Proposal: I would add after the Example 7.1 on MPI-3.1 page 293 line 42 If ndims is zero, then nnodes must be one, and the argument dims will be ignored, i.e., there will be no output. Changelog in "Changes in MPI-4.0": Section 7.5.2 on page 792. MPI_DIMS_CREATE was extended to additionally allow a zero-dimensional Cartesian topology, i.e., input ndims==0 together with nnodes==1. Bill, please can you provide the ticket/issue/... with probably better wording ... Rolf ----- Original Message ----- > From: "wgropp" <wgropp(a)illinois.edu> > To: "Comments on the MPI Standard" <mpi-comments(a)lists.mpi-forum.org> > Sent: Wednesday, November 9, 2016 7:04:44 PM > Subject: Re: [Mpi-comments] MPI_Dims_create(..., ndims=0, ...) semantic ? > I agree with the analysis of the output but disagree with the conclusion - to > make the behavior consistent with that of MPI_Cart_create, ndim == 0 should be > permitted (with nnodes == 1) but there is, as noted, no output other than a > return value / error value set of MPI_SUCCESS. Otherwise the use of > MPI_Dims_create with MPI_Cart_create in the general case looks like > > if (ndim > 0) MPI_Dims_create(…) > MPI_Cart_create(…) > > while the intent of the changes for MPI_Cart_create was to allow > > MPI_Dims_create(…) > MPI_Cart_create(…) > > even if ndim == 0. > > 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 9, 2016, at 9:17 AM, Rolf Rabenseifner < [ mailto:[email protected] | > rabenseifner(a)hlrs.de ] > wrote: > > > > We added all that the MPI_CART_... routines work fine with ndims==0. > > We oversaw that MPI_DIMS_CREATE is also a candidate for ndims==0. > > Reading the standard, I would say that MPI_DIMS_CREATE > - with ndims==0 can never have any output, because > the ndims Array has no element, > - with ndims==0 and nnodes != 1 is erronous > because a zero-dim-cart-topology has alwas exactly one node > (and erronous implies always undefined behavior, > i.e., the MPI library may catch or ignore this error), > - with ndims==0 and nnodes == 1 would be okay but would not > produce any output (because ndims has no entries), > - but compared to the other CART routines where ndims==0 > behaviour is always explicitely specified, I would conclude > that MPI_DIMS_CREATE with ndims==0 has always undefined > behavior, i.e., that also ndims==0 and nnodes == 1 may be > treated by the MPI library as erronous. > > Therefore, I would recommend to clarify the standard by > defining ndims of MPI_DIMS_CREATE as "positive integer" > instead of only "integer". > > Rolf > > ----- Original Message ----- > > > From: "wgropp" < [ mailto:[email protected] | wgropp(a)illinois.edu ] > > To: "Comments on the MPI Standard" < [ mailto:[email protected] | > mpi-comments(a)lists.mpi-forum.org ] > > Sent: Wednesday, November 9, 2016 3:18:10 PM > Subject: Re: [Mpi-comments] MPI_Dims_create(..., ndims=0, ...) semantic ? > > > > 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 < [ [ mailto:[email protected] > | mailto:[email protected] ] | > [ mailto:[email protected] | gilles(a)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 > > _______________________________________________ > mpi-comments mailing list > [ [ mailto:[email protected] | > mailto:[email protected] ] | [ > mailto:[email protected] | mpi-comments(a)lists.mpi-forum.org ] ] > [ https://lists.mpi-forum.org/mailman/listinfo/mpi-comments | > https://lists.mpi-forum.org/mailman/listinfo/mpi-comments ] > > > _______________________________________________ > mpi-comments mailing list > mpi-comments(a)lists.mpi-forum.org > https://lists.mpi-forum.org/mailman/listinfo/mpi-comments > > -- > Dr. Rolf Rabenseifner . . . . . . . . . .. email [ mailto:[email protected] | > rabenseifner(a)hlrs.de ] > High Performance Computing Center (HLRS) . phone ++49(0)711/685-65530 > University of Stuttgart . . . . . . . . .. fax ++49(0)711 / 685-65832 > Head of Dpmt Parallel Computing . . . [ http://www.hlrs.de/people/rabenseifner | > www.hlrs.de/people/rabenseifner ] > Nobelstr. 19, D-70550 Stuttgart, Germany . . . . (Office: Room 1.307) > _______________________________________________ > mpi-comments mailing list > [ mailto:[email protected] | mpi-comments(a)lists.mpi-forum.org ] > https://lists.mpi-forum.org/mailman/listinfo/mpi-comments > > > _______________________________________________ > mpi-comments mailing list > mpi-comments(a)lists.mpi-forum.org > https://lists.mpi-forum.org/mailman/listinfo/mpi-comments -- Dr. Rolf Rabenseifner . . . . . . . . . .. email rabenseifner(a)hlrs.de High Performance Computing Center (HLRS) . phone ++49(0)711/685-65530 University of Stuttgart . . . . . . . . .. fax ++49(0)711 / 685-65832 Head of Dpmt Parallel Computing . . . www.hlrs.de/people/rabenseifner Nobelstr. 19, D-70550 Stuttgart, Germany . . . . (Office: Room 1.307) _______________________________________________ mpi-comments mailing list mpi-comments(a)lists.mpi-forum.org https://lists.mpi-forum.org/mailman/listinfo/mpi-comments

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Re: [Mpi-comments] MPI_Dims_create(..., ndims=0, ...) semantic ?
by William Gropp 09 Nov '16

09 Nov '16

I agree with the analysis of the output but disagree with the conclusion - to make the behavior consistent with that of MPI_Cart_create, ndim == 0 should be permitted (with nnodes == 1) but there is, as noted, no output other than a return value / error value set of MPI_SUCCESS. Otherwise the use of MPI_Dims_create with MPI_Cart_create in the general case looks like if (ndim > 0) MPI_Dims_create(…) MPI_Cart_create(…) while the intent of the changes for MPI_Cart_create was to allow MPI_Dims_create(…) MPI_Cart_create(…) even if ndim == 0. 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 9, 2016, at 9:17 AM, Rolf Rabenseifner <rabenseifner(a)hlrs.de> wrote: > We added all that the MPI_CART_... routines work fine with ndims==0. > > We oversaw that MPI_DIMS_CREATE is also a candidate for ndims==0. > > Reading the standard, I would say that MPI_DIMS_CREATE > - with ndims==0 can never have any output, because > the ndims Array has no element, > - with ndims==0 and nnodes != 1 is erronous > because a zero-dim-cart-topology has alwas exactly one node > (and erronous implies always undefined behavior, > i.e., the MPI library may catch or ignore this error), > - with ndims==0 and nnodes == 1 would be okay but would not > produce any output (because ndims has no entries), > - but compared to the other CART routines where ndims==0 > behaviour is always explicitely specified, I would conclude > that MPI_DIMS_CREATE with ndims==0 has always undefined > behavior, i.e., that also ndims==0 and nnodes == 1 may be > treated by the MPI library as erronous. > > Therefore, I would recommend to clarify the standard by > defining ndims of MPI_DIMS_CREATE as "positive integer" > instead of only "integer". > > Rolf > > ----- Original Message ----- >> From: "wgropp" <wgropp(a)illinois.edu> >> To: "Comments on the MPI Standard" <mpi-comments(a)lists.mpi-forum.org> >> Sent: Wednesday, November 9, 2016 3:18:10 PM >> Subject: Re: [Mpi-comments] MPI_Dims_create(..., ndims=0, ...) semantic ? > >> 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 < [ mailto:[email protected] | >> gilles(a)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 >> >> _______________________________________________ >> mpi-comments mailing list >> [ mailto:[email protected] | mpi-comments(a)lists.mpi-forum.org ] >> https://lists.mpi-forum.org/mailman/listinfo/mpi-comments >> >> >> _______________________________________________ >> mpi-comments mailing list >> mpi-comments(a)lists.mpi-forum.org >> https://lists.mpi-forum.org/mailman/listinfo/mpi-comments > > -- > Dr. Rolf Rabenseifner . . . . . . . . . .. email rabenseifner(a)hlrs.de > High Performance Computing Center (HLRS) . phone ++49(0)711/685-65530 > University of Stuttgart . . . . . . . . .. fax ++49(0)711 / 685-65832 > Head of Dpmt Parallel Computing . . . www.hlrs.de/people/rabenseifner > Nobelstr. 19, D-70550 Stuttgart, Germany . . . . (Office: Room 1.307) > _______________________________________________ > mpi-comments mailing list > mpi-comments(a)lists.mpi-forum.org > https://lists.mpi-forum.org/mailman/listinfo/mpi-comments _______________________________________________ mpi-comments mailing list mpi-comments(a)lists.mpi-forum.org https://lists.mpi-forum.org/mailman/listinfo/mpi-comments

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Re: [Mpi-comments] MPI_Dims_create(..., ndims=0, ...) semantic ?
by Rolf Rabenseifner 09 Nov '16

09 Nov '16

We added all that the MPI_CART_... routines work fine with ndims==0. We oversaw that MPI_DIMS_CREATE is also a candidate for ndims==0. Reading the standard, I would say that MPI_DIMS_CREATE - with ndims==0 can never have any output, because the ndims Array has no element, - with ndims==0 and nnodes != 1 is erronous because a zero-dim-cart-topology has alwas exactly one node (and erronous implies always undefined behavior, i.e., the MPI library may catch or ignore this error), - with ndims==0 and nnodes == 1 would be okay but would not produce any output (because ndims has no entries), - but compared to the other CART routines where ndims==0 behaviour is always explicitely specified, I would conclude that MPI_DIMS_CREATE with ndims==0 has always undefined behavior, i.e., that also ndims==0 and nnodes == 1 may be treated by the MPI library as erronous. Therefore, I would recommend to clarify the standard by defining ndims of MPI_DIMS_CREATE as "positive integer" instead of only "integer". Rolf ----- Original Message ----- > From: "wgropp" <wgropp(a)illinois.edu> > To: "Comments on the MPI Standard" <mpi-comments(a)lists.mpi-forum.org> > Sent: Wednesday, November 9, 2016 3:18:10 PM > Subject: Re: [Mpi-comments] MPI_Dims_create(..., ndims=0, ...) semantic ? > 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 < [ mailto:[email protected] | > gilles(a)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 > > _______________________________________________ > mpi-comments mailing list > [ mailto:[email protected] | mpi-comments(a)lists.mpi-forum.org ] > https://lists.mpi-forum.org/mailman/listinfo/mpi-comments > > > _______________________________________________ > mpi-comments mailing list > mpi-comments(a)lists.mpi-forum.org > https://lists.mpi-forum.org/mailman/listinfo/mpi-comments -- Dr. Rolf Rabenseifner . . . . . . . . . .. email rabenseifner(a)hlrs.de High Performance Computing Center (HLRS) . phone ++49(0)711/685-65530 University of Stuttgart . . . . . . . . .. fax ++49(0)711 / 685-65832 Head of Dpmt Parallel Computing . . . www.hlrs.de/people/rabenseifner Nobelstr. 19, D-70550 Stuttgart, Germany . . . . (Office: Room 1.307) _______________________________________________ mpi-comments mailing list mpi-comments(a)lists.mpi-forum.org https://lists.mpi-forum.org/mailman/listinfo/mpi-comments

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Re: [Mpi-comments] MPI_Dims_create(..., ndims=0, ...) semantic ?
by William Gropp 09 Nov '16

09 Nov '16

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(a)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 > > _______________________________________________ > mpi-comments mailing list > mpi-comments(a)lists.mpi-forum.org > https://lists.mpi-forum.org/mailman/listinfo/mpi-comments _______________________________________________ mpi-comments mailing list mpi-comments(a)lists.mpi-forum.org https://lists.mpi-forum.org/mailman/listinfo/mpi-comments

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MPI_Dims_create(..., ndims=0, ...) semantic ?
by Gilles Gouaillardet 08 Nov '16

08 Nov '16

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 _______________________________________________ mpi-comments mailing list mpi-comments(a)lists.mpi-forum.org https://lists.mpi-forum.org/mailman/listinfo/mpi-comments

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