Re: [eigen] help: eigen3.3 desn't imporve the speed with multitreading.

[ztdepyahoo <ztdepyahoo@xxxxxxxxx>]

yes, -fopenmp is in the flag. I have tried many times. it doen'twork.

	ztdepyahoo
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On 9/10/2020 20:47，Gael Guennebaud<gael.guennebaud@xxxxxxxxx> wrote：

Hi,

make sure to use Eigen's head, and to compile with OpenMP enabled on your compiler, for instance with -fopenmp with GCC.

Gaël

On Thu, Sep 10, 2020 at 6:25 AM ztdepyahoo <ztdepyahoo@xxxxxxxxx> wrote:

I have set the tread =12 in the program .  Eigen::nbThreads( ) also feedbacks correct number. 

but the speed of solution seems doesn't change. 

what is the reason.

Regards

    Eigen::setNbThreads(12);

     int nthreads = Eigen::nbThreads( );

     std::cout << "THREADS = " << nthreads <<std::ends; // returns '1'

    BiCGSTAB<SparseMatrix<double, RowMajor>, IncompleteLUT<double>> solver;

    solver.setTolerance(1e-10);

    solver.setMaxIterations(1000);

    solver.compute(A);

    VectorXd x = solver.solve(b);

	ztdepyahoo
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