Thanks Josh! That was helpful.
-- Nilesh.
On Sun, Sep 19, 2010 at 1:29 AM, Josh Milthorpe
<josh.miltho...@anu.edu.au> wrote:
> Hi Nilesh,
>
> browsing the list archive, I noticed nobody had yet answered this one -
> sorry for the silence!
>
> The Array classes have been in a state of flux over recent months, with
> significant performance improvements and changes to the distributed
> object model for X10 2.1. Unfortunately, while this work has been
> occurring, some of the nice Region operations (union, intersection,
> complement) have been disabled. This means that it is currently more
> complicated to express the sort of Region manipulation you are describing.
>
> Once Region.union(...) has been restored, you might express the
> combination of two rectangular subregions of a matrix as:
>
> val rowOne = Region.make([i1..i1, 0..N-1]);
> val rowTwo = Region.make([i2..i2, 0..N-1]);
> val combined = rowOne || rowTwo;
>
> Note that in the above, the rows are still 2-D regions, in which the
> first dimension is of size 1. This is necessary to allow them to be
> combined in a 2-D union.
>
> For now, the subregions must be treated separately, 'pasting' them
> together using Point translations. The example below is a function to
> eliminate a selected row from a matrix, as might be done in calculating
> e.g. the Laplace expansion.
>
> def eliminateRow(source : DistArray[Double](2), row : Int) {
> val resultRegion = [source.region.min(0)..source.region.max(0)-1,
> source.region.min(1)..source.region.max(1)];
> val result = DistArray.make[Double](source.dist | resultRegion);
> val rowsAbove = Region.make([source.region.min(0)..row-1,
> source.region.min(1)..source.region.max(1)]);
> val rowsBelow = Region.make([row+1..source.region.max(0),
> source.region.min(1)..source.region.max(1)]);
> finish ateach (p in result | rowsAbove) {
> result(p) = source(p);
> }
> // remaining rows must be shifted up by one
> val shift = Point.make(1, 0);
> finish ateach (p in result | (rowsBelow-shift)) {
> result(p) = at (source.dist(p+shift)) {source(p+shift)};
> }
> return result;
> }
>
> Note that this could be simplified given certain assumptions about the
> distribution - for example, if the matrix were block distributed in
> dimension 1 (_not_ in dimension 0), the 'at (source.dist(p+shift))'
> would not be required. If the entire matrix were stored as an Array at
> a single place, data could be efficiently copied in bulk using
> Array.copy(...).
>
> I hope some of this is useful.
>
> Cheers,
>
> Josh
>
>
> Nilesh Mahajan wrote:
>> Hi,
>>
>> I was wondering if there is a way to combine two or more 1-dimensional
>> distributions to form a 2-D distribution. For example, I would like to
>> select arbitrary rows from a matrix and form a sub-matrix out of it.
>> The rows can be non-contiguous and I don't know them statically.
>>
>> Thanks,
>> Nilesh.
>>
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