Dear David,
Thank you very much for your very beneficial reply, it helped me a lot
so basically what I did right now
is that I have a matrix M of type (DistArray) which contains Array[double]
in which these arrays are distributed
and a vector V of type (DistArray) which also contains Array[double] and its
also distributed as follows:
M : V:
--------------------------- -------
| A B I J | | X |
| C D K L | | Y |
| E F M N | | Z |
| G H O P | | R |
--------------------------- -------
where AB,C,D,E,F,G,H are in place 0 also X,Y
and I,J,K,L,M,N,O,P are in place 1 also Z,R
so that multiplication could happen locally
but my problem is when I want to sum up all the results in a global linear
array called result which is at place 0
when ever i want to add those elements that reside at place 1 to the values
of the result array, a bad place exception occurs.
so how can I pass an array (or the values of the array) that resides at
place 1 to the result array that resides at place 0?
Thank you
Mohammed @KAUST
On Fri, Jul 9, 2010 at 1:33 PM, David P Grove <gro...@us.ibm.com> wrote:
>
> Hi,
>
> Trying to paraphrase the question, I think you are asking what X10
> classes provided by the standard library support indexed addressing (a
> (i,j.k)) and store their elements in memory in a format that is compatible
> with passing a pointer to the elements (or a subset of the elements) to a
> native C/BLAS routine that is expecting a C-style []. Is this right?
>
> In 2.0.4, there are two primitive data types that support this: Rail
> and ValRail. Both of these have a raw() method that gets you a pointer to
> the C-level storage. Built on top of Rail we also have Array, DistArray,
> and DistributedRail. Array is the simplest of these, it is a single-place
> k-dimensional array that maps its data elements into a backing Rail using a
> row-major layout (like C, not like Fortran). DistArray is a multi-place
> k-dimensional array that divides the data elements (according to the Dist
> chose: block, blockCyclic, etc) among places and then in each place maps
> the data elements into a different backing rail using a row-major layout.
> For both Array and DistArray you can use the raw() method (which is public
> for Array, but not for DistArray) to get the backing Rail with the data and
> pass it to native code.
> DistributedRail is a little different. Instead of mapping each
> index
> to a single data value found in one place, it maps each index to a
> different data element in each place. It gives you the abstraction of a
> different Rail in each place that have the same indices, but potentially
> different data elements at each place. The other interesting piece of
> DistributedRail is that it provides collective reduction operations that
> allow you to combine the Rails from each place. Since the backing data
> structure here is a Rail, you can pass it to native routines. You could
> think of DistArray as providing a global-index and DistributedRail of
> providing a local-index API to approximately the same low-level storage: a
> Rail at each place that is used to store data elements.
>
> In 2.0.5 (and the current svn head) things are a little different.
> We've introduced a lower-level IndexedMethodChunk class, and Array is now
> built on top of it instead of ontop of Rail. Similar concepts apply
> though.
>
> If you wanted to, you can also define a DistArray of some other
> object/indexed data structure. For example of this, you can take a look at
> our SSCA1 implementation
> (https://x10.svn.sf.net/svnroot/x10/benchmarks/trunk/SSCA1/x10). Here
> there's a DistArray that contains 1 point for each place. At each place
> the array contains a pointer to an object that in turn contains several
> Rail and ValRail objects. You could also have a DistArray[Array[double]] if
> you want to think about a local-index space at each place instead of a
> global-index space across the whole DistArray.
>
> Hope this is helpful. If I missed the point of your question, please let
> me know and I'll try again.
>
> --dave
>
>
>
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--
Thank you for your concern.
Regards,
Mohammed El Sayed
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