[mlpack-git] [mlpack/mlpack] parallel sgd (#603)

[Stephen Tu]

> +  sumIterate.zeros();
> +
> +
> +
> +  #pragma omp parallel  shared(sumIterate,halt) private(it) 
> +  {
> +    it=1; 
> +    while(it!=maxIterations && halt != true)
> +    {
> +      it++;
> +
> +      int th_num=omp_get_thread_num(); //thread number is stored in which the thread is running. 
> +      arma::mat gradient(iterate.n_rows, iterate.n_cols);  //To make gradient private to each thread it is declared here.
> +      int selectedFunction;
> +    
> +      selectedFunction=std::rand()%numFunctions;

Calling `std::rand()` is problematic here. Either (a) it is not thread safe, in which case who knows how random these numbers will be, or (b) it is, and that will be a point of slowdown. Whether or not `std::rand()` is threadsafe is *implementation-specific* (see e.g. http://en.cppreference.com/w/cpp/numeric/random/rand). The easiest fix is to allocate seeds for each thread and use a thread local PRNG. 

---
You are receiving this because you are subscribed to this thread.
Reply to this email directly or view it on GitHub:
https://github.com/mlpack/mlpack/pull/603/files/a981f8322e84ec06a349b80d261639a282f4f7c5#r58914680
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://mailman.cc.gatech.edu/pipermail/mlpack-git/attachments/20160407/95249556/attachment.html>