[Trilinos-Users] [EXTERNAL] Re: Best practice to modify elements of a Tpetra::Vector with openmp?

[Wen Yan]

Thanks a lot!

Wen Yan


> On Jun 8, 2017, at 6:58 PM, Hoemmen, Mark <mhoemme at sandia.gov> wrote:
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> On 6/8/17, 3:04 PM, "Wen Yan" <wenyan4work at gmail.com> wrote:
>> Could you please also confirm the following?
>> 
>> 1. x_2d is a 2D Kokkos::View with Kokkos::LayoutLeft, and the entries x_2d(i,c) are continuous in memory for continuous index i. Here i ranges from 0 to local length - 1, and c ranges from 0 to the number of vectors in the Tpetra::MultiVector - 1
> 
> Yes.
> 
>> 
>> 2. x_2d is safe to use with openmp, like:
>> for (int c = 0; c < x_2d.dimension_1(); c++) {
>> #pragma omp parallel for
>>   for (int i = 0; i < x_2d.dimension_0(); i++) {
>>     const double temp = x_2d(i, c);
>>     x_2d(i, c) = temp < 0 ? 0 : temp;
>>   }
>> }
> 
> Yes.  Also, why not use Kokkos?
> 
> const int numCols = x_2d.dimension_1 ();
> for (int c = 0; c < numCols; ++c) {
>  Kokkos::parallel_for (
>    Kokkos::RangePolicy<Kokkos::OpenMP, int> (0, x_2d.dimension_0 ()), 
>    KOKKOS_LAMBDA (const int r) {
>      const double temp = x_2d(r,c);
>      x_2d(r,c) = temp < 0.0 ? 0.0 : temp;  
>    });
> }
> 
>> 3. For read-only access there is no need to call modify<Kokkos::HostSpace>()
> 
> That is correct.  The example should explain.
> 
> mfh