Le 19/08/2021 à 17:04, Naeem Khoshnevis a écrit :
Thank you so much, everyone, for responding to this email.
Dirk,
* I didn't think about testing _equality_ of doubles because the
numbers are significantly different (e.g., instead of 0.5, chooses
1.5). However, that is a valid point, and I should be aware of that.
* You are right about the serial runs. Whenever I deactivate OpenMP,
the results are correct.
Serguei,
* Thanks for the comments. Yes, I agree. It seems outer is a better
option. We have started with outer. However, outer builds the
entire matrix of differences first, then finds the minimum index.
In our application, it requires 200 GB of memory to build that matrix.
This problem was hardly foreseeable from examples in hand. But I still
think that a pure R solution can be a runner:
ac=a*sc
bc=b*sc
out=vapply(seq_along(bc), function(i)
which.min(abs(ac-bc[i])+cd[i]), integer(1))
Best,
Serguei.
* Rcpp does the job with around 10 MB. That is why I switched to
Rcpp. Please let me know your thoughts.
Iñaki,
* Thanks for your suggestion. Yes, the problem is shared values, and
it resolved the issue. I really appreciate it.
Best regards,
Naeem
On Thu, Aug 19, 2021 at 4:56 AM Iñaki Ucar <iu...@fedoraproject.org
<mailto:iu...@fedoraproject.org>> wrote:
On Thu, 19 Aug 2021 at 04:53, Dirk Eddelbuettel <e...@debian.org
<mailto:e...@debian.org>> wrote:
>
>
> Naeem,
>
> I would simplify, simplify, simplify -- as 'Rcpp FAQ 7.31'
reminds us all,
> testing _equality_ of doubles is challenging anyway.
>
> Besides, it may make sense to would ascertain first you get what
you want in
> _purely serial modes_ and then move to OpenMP.
Exactly. Serial execution should be fine. I.e., if you set the number
of threads to 1, then all platforms will return the same result.
However, you have defined a number of variables outside the parallel
region, and then you modify them inside the parallel region. OpenMP
takes those variables as shared by default, which leads to the
unexpected results you are getting. You need to tell OpenMP that those
variables are threadprivate. Or you could just define them inside the
parallel region, so that OpenMP knows that they are private without
additional hints.
--
Iñaki Úcar
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