The subarray creation is an multi-dimension extension of the vector type. You can see it as a vector of vector of vector and so on, one vector per dimension. The stride array is used to declare on each dimension what is the relative displacement (in number of elements) from the beginning of the dimension array.
It is important to use regular type creation when you can take advantage of such regularity instead of resorting to use of struct or h*. This insure better packing/unpacking performance, as well as possible future support for one-sided communications. George. > On Jan 15, 2015, at 19:31, Gus Correa <g...@ldeo.columbia.edu> wrote: > > I never used MPI_Type_create_subarray, only MPI_Type_Vector. > What I like about MPI_Type_Vector is that you can define a stride, > hence you can address any regular pattern in memory. > However, it envisages the array layout in memory as a big 1-D array, > with a linear index progressing in either Fortran or C order. > > Somebody correct me please if I am wrong, but at first sight MPI_Type_Vector > sounds more flexible to me than MPI_Type_create_subarray, exactly because the > latter doesn't have strides. > > The downside is that you need to do some index arithmetic to figure > the right strides, etc, to match the corresponding > Fortran90 array sections. > > There are good examples in the "MPI - The complete reference" books I > suggested to you before (actually in vol 1). > > Online I could find the two man pages (good information, but no example): > > http://www.open-mpi.org/doc/v1.8/man3/MPI_Type_vector.3.php > http://www.open-mpi.org/doc/v1.8/man3/MPI_Type_create_subarray.3.php > > There is a very simple 2D example of MPI_Type_vector using strides here: > > https://computing.llnl.gov/tutorials/mpi/#Derived_Data_Types > > and a similar one here: > > http://static.msi.umn.edu/tutorial/scicomp/general/MPI/content6.html > > Gus Correa > >> On 01/15/2015 06:53 PM, Diego Avesani wrote: >> dear George, dear Gus, dear all, >> Could you please tell me where I can find a good example? >> I am sorry but I can not understand the 3D array. >> >> >> Really Thanks >> >> Diego >> >> >> On 15 January 2015 at 20:13, George Bosilca <bosi...@icl.utk.edu >> <mailto:bosi...@icl.utk.edu>> wrote: >> >> >>> On Jan 15, 2015, at 06:02 , Diego Avesani <diego.aves...@gmail.com >>> <mailto:diego.aves...@gmail.com>> wrote: >>> >>> Dear Gus, Dear all, >>> Thanks a lot. >>> MPI_Type_Struct works well for the first part of my problem, so I >>> am very happy to be able to use it. >>> >>> Regarding MPI_TYPE_VECTOR. >>> >>> I have studied it and for simple case it is clear to me what id >>> does (at least I believe). Foe example if I have a matrix define as: >>> REAL, ALLOCATABLE (AA(:,:)) >>> ALLOCATE AA(100,5) >>> >>> I could send part of it defining >>> >>> CALL MPI_TYPE_VECTOR(5,1,5,MPI_DOUBLE_PRECISION,/MY_NEW_TYPE/) >>> >>> after that I can send part of it with >>> >>> CALL MPI_SEND( AA(1:/10/,:), /10/, /MY_NEW_TYPE/, 1, 0, >>> MPI_COMM_WORLD ); >>> >>> Have I understood correctly? >>> >>> What I can do in case of three dimensional array? for example >>> AA(:,:,:), I am looking to MPI_TYPE_CREATE_SUBARRAY. >>> Is that the correct way? >>> >>> Thanks again >> >> Indeed, using the subarray is the right approach independent on the >> number of dimensions of the data (you can use it instead of >> MPI_TYPE_VECTOR as well). >> >> George. >> >> >>> >>> >>> >>> >>> Diego >>> >>> >>> On 13 January 2015 at 19:04, Gus Correa <g...@ldeo.columbia.edu >>> <mailto:g...@ldeo.columbia.edu>> wrote: >>> >>> Hi Diego >>> I guess MPI_Type_Vector is the natural way to send and receive >>> Fortran90 array sections (e.g. your QQMLS(:,50:100,:)). >>> I used that before and it works just fine. >>> I think that is pretty standard MPI programming style. >>> I guess MPI_Type_Struct tries to emulate Fortran90 and C >>> structures >>> (as you did in your previous code, with all the surprises >>> regarding alignment, etc), not array sections. >>> Also, MPI type vector should be more easy going (and probably >>> more efficient) than MPI type struct, with less memory >>> alignment problems. >>> I hope this helps, >>> Gus Correa >>> >>> PS - These books have a quite complete description and several >>> examples >>> of all MPI objects and functions, including MPI types (native >>> and user defined): >>> http://mitpress.mit.edu/books/__mpi-complete-reference-0 >>> <http://mitpress.mit.edu/books/mpi-complete-reference-0> >>> http://mitpress.mit.edu/books/__mpi-complete-reference-1 >>> <http://mitpress.mit.edu/books/mpi-complete-reference-1> >>> >>> [They cover MPI 1 and 2. I guess there is a new/upcoming book >>> with MPI 3, but for what you're doing 1 and 2 are more than >>> enough.] >>> >>> >>> On 01/13/2015 09:22 AM, Diego Avesani wrote: >>> >>> Dear all, >>> >>> I had some wonderful talking about MPI_type_create_struct adn >>> isend\irecv with >>> Gilles, Gustavo, George, Gus, Tom and Jeff. Now all is >>> more clear and my >>> program works. >>> >>> Now I have another question. In may program I have matrix: >>> >>> /QQMLS(:,:,:) /that is allocate as >>> >>> /ALLOCATE(QQMLS(9,npt,18)/), where npt is the number of >>> particles >>> >>> QQMLS is double precision. >>> >>> I would like to sent form a CPU to another part of it, for >>> example, >>> sending QQMLS(:,50:100,:). I mean sending the QQMLS of the >>> particles >>> between 50 to 100. >>> I suppose that i could use MPI_Type_vector but I am not >>> sure. The >>> particle that I want to sent could be from 25 to 50 ecc.. >>> ecc..so >>> blocklength changes everytime. >>> >>> Do I have to use MPI_type_create_struct? >>> Do I have correctly understood MPI_Type_vector? >>> >>> Thanks a lot >>> >>> >>> Diego >>> >>> >>> >>> _________________________________________________ >>> users mailing list >>> us...@open-mpi.org <mailto:us...@open-mpi.org> >>> Subscription: >>> http://www.open-mpi.org/__mailman/listinfo.cgi/users >>> <http://www.open-mpi.org/mailman/listinfo.cgi/users> >>> Link to this post: >>> >>> http://www.open-mpi.org/__community/lists/users/2015/01/__26171.php >>> <http://www.open-mpi.org/community/lists/users/2015/01/26171.php> >>> >>> >>> _________________________________________________ >>> users mailing list >>> us...@open-mpi.org <mailto:us...@open-mpi.org> >>> Subscription: >>> http://www.open-mpi.org/__mailman/listinfo.cgi/users >>> <http://www.open-mpi.org/mailman/listinfo.cgi/users> >>> Link to this post: >>> http://www.open-mpi.org/__community/lists/users/2015/01/__26172.php >>> <http://www.open-mpi.org/community/lists/users/2015/01/26172.php> >>> >>> >>> _______________________________________________ >>> users mailing list >>> us...@open-mpi.org <mailto:us...@open-mpi.org> >>> Subscription: http://www.open-mpi.org/mailman/listinfo.cgi/users >>> Link to this post: >>> http://www.open-mpi.org/community/lists/users/2015/01/26184.php >> >> >> _______________________________________________ >> users mailing list >> us...@open-mpi.org <mailto:us...@open-mpi.org> >> Subscription: http://www.open-mpi.org/mailman/listinfo.cgi/users >> Link to this post: >> http://www.open-mpi.org/community/lists/users/2015/01/26192.php >> >> >> >> >> _______________________________________________ >> users mailing list >> us...@open-mpi.org >> Subscription: http://www.open-mpi.org/mailman/listinfo.cgi/users >> Link to this post: >> http://www.open-mpi.org/community/lists/users/2015/01/26193.php > > _______________________________________________ > users mailing list > us...@open-mpi.org > Subscription: http://www.open-mpi.org/mailman/listinfo.cgi/users > Link to this post: > http://www.open-mpi.org/community/lists/users/2015/01/26194.php
