You would have been 'already there' through iteration if you had used
an "ateach" loop:
public static def main(args:Rail[String]!){
val R = 1..4; // The inferred type here is Region(1){rect}
val D = Dist.makeCyclic(R); // The inferred type here is
Dist{region==R)
val data_squares = Array.make[Int](D, ((i):Point(1)) => i*i);
ateach (val p in D) { // The inferred type here is Point(1)
Console.OUT.println( "Array index: " + p + " distributed place :" +
D(p));
// Note that, due to the ateach loop, D(p)==here,
// so now you're 'already there'
Console.OUT.println( "Array element: " + data_squares(p));
}
}
Hope this helps.
Igor
Haris H <hha...@gmail.com> wrote on 03/29/2010 09:01:27 PM:
> Thank you very much guys,
> I had this idea that "at" is not needed since I am 'already there'
through
> iteration.
>
> I may come back for more stuff later but this definitely clears much of
my
> confusion.
>
> Thank you again.
>
> Haris
>
>
>
>
>
> On Sun, Mar 28, 2010 at 9:00 PM, Igor Peshansky <ig...@us.ibm.com>
wrote:
>
> > This is a typical X10 beginner mistake: you specify types that
> > are too imprecise. You cannot index into an Array with a Point
> > unless it can be statically proven that the rank of that Point
> > is exactly equal to the rank of the Array's region.
> >
> > The best rule of thumb is to let X10 infer the types for you.
> > Barring that, you should look carefully at the methods you call
> > to ensure that the rank is propagated correctly. Incidentally,
> > to get efficient iteration, you'd want to propagate other
> > pr0operties of the Array's region (e.g., the fact that it's
> > rectangular).
> >
> > Another problem is that array elements have to be accessed in
> > the place where they live (as specified by the distribution).
> > This is not something that can be checked statically, but you
> > will get a runtime exception if this rule is violated.
> >
> > So, you should rewrite your code as follows:
> >
> > public static def main(args:Rail[String]!){
> > val R = 1..4; // The inferred type here is Region(1){rect}
> > val D = Dist.makeCyclic(R); // The inferred type here is
> > Dist{region==R)
> >
> > val data_squares = Array.make[Int](D, ((i):Point(1)) => i*i);
> >
> > for (val p in D) { // The inferred type here is Point(1)
> > Console.OUT.println( "Array index: " + p + " distributed place
:" +
> > D(p));
> >
> > // this is the problem part, but this is how I understood arrays
> >
> > Console.OUT.println( "Array element: " + at (D(p))
data_squares(p));
> >
> > // how can I access e.g. data_squares(3) and its value and place.
> > // using 2.0 java back end on eclipse
> > }
> > }
> >
> > Vijay already covered most of these points, but one that I wanted
> > to bring up is that, unless you know exactly what the type is,
> > better let the type system infer the most precise type. In
> > particular, if you'd left the type of D as just Dist, the iteration
> > would have been woefully inefficient (which would have hurt your
> > peformance for larger arrays).
> >
> > As Vijay said, we are working on relaxing that requirement.
> > Igor
> >
> > Haris H <hha...@gmail.com> wrote on 03/28/2010 03:57:47 PM:
> >
> > > Hi guys,
> > > can somebody clear this up for me please.
> > > I can not get my head around this element manipulation in
distributed
> > arrays
> > > in 2.0.
> > >
> > > Here is the overly simplified code but represents my problem,
> > > so please tell me what am I doing wrong and what it should be.
> > >
> > > I am having trouble understanding accessing elements of the array
and
> > their
> > > distributed location.
> > >
> > > Thank you.
> > >
> > > public static def main(args:Rail[String]!){
> > >
> > > R: Region = 1..4;
> > > D: Dist = Dist.makeCyclic(R);
> > >
> > > val data_squares = Array.make[Int](D, ((i):Point) => i*i);
> > >
> > > for (val p: Point in D) {
> > > Console.OUT.println( "Array index: " + p + " distributed
place :"
> > +
> > > D(p));
> > >
> > > // this is the problem part, but this is how I understood
arrays
> > >
> > > Console.OUT.println( "Array element: " + data_squares(p));
> > >
> > > // how can I access e.g. data_squares(3) and its value and
place.
> > > // using 2.0 java back end on eclipse
> > > }
> > > }
--
Igor Peshansky (note the spelling change!)
IBM T.J. Watson Research Center
X10: Parallel Productivity and Performance (http://x10-lang.org/)
XJ: No More Pain for XML's Gain (http://www.research.ibm.com/xj/)
"I hear and I forget. I see and I remember. I do and I understand" --
Confucius
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