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Subject: Re: [ublas] profiling shows most time is consumed by indexing_matrix_assign
From: Nasos Iliopoulos (nasos_i_at_[hidden])
Date: 2010-04-10 20:31:49
Hi Heikko,
did you check if you have nested products? (those may be hidden sometimes if you pass expressions around) Take a look at the very last item in http://www.boost.org/doc/libs/1_42_0/libs/numeric/ublas/doc/index.htm.
The indexing_matrix_assign is the main function that is called when you assign an expression to a matrix in ublas, so everything passes through that. And remember in ublas A+B (with A and B matrices) is an expression in ublas, not a matrix, it becomes a matrix when you assign it to something.
Also try to play with -DBOOST_UBLAS_MOVE_SEMANTICS (http://www.boost.org/doc/libs/1_42_0/libs/numeric/ublas/doc/options.htm) and noalias() (http://www.boost.org/doc/libs/1_41_0/libs/numeric/ublas/doc/operations_overview.htm) , to see if those help.
Best regards
Nasos
> From: heiko_at_[hidden]
> To: ublas_at_[hidden]
> Date: Fri, 9 Apr 2010 18:20:41 +0200
> Subject: [ublas] profiling shows most time is consumed by indexing_matrix_assign
>
> Dear all,
>
> I have just recently begun to use uBLAS to do some numerics, solving a
> system of ordinary linear differential equations. The ODE solver
> repeatedly invokes a function that computes the right hand side of the
> ODE, and that contains almost the whole computational effort. In this
> function, I have about 8 matrix-matrix multiplications (with prod()) and
> about the same number of additions/subtractions of matrices or
> multiplications with a scalar. The involved matrices are dense with
> std::complex<double> entries and are of dimension 800x800.
>
> The program, especially the evaluation of the rhs function, seems to be
> running fairly slow and profiling with gprof shows that the rhs
> evaluation takes 95%
> of the computation time. Deeper inspection shows that two
> versions of indexing_matrix_assign() account for almost all
> of the time needed. Now comes my question: Is this the expected
> behaviour for the described situation?
>
> Some additional information: I am using uBLAS 1.41.0 with NDEBUG set to
> 1.
>
> Any help is appreciated.
>
> Best regards,
>
> Heiko Schröder
>
>
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> Sent to: nasos_i_at_[hidden]
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