Re: [eigen] Optimization advice for a specific expression

[Christoph Hertzberg <chtz@xxxxxxxxxxxxxxxxxxxxxxxx>]

You could also try
  I4x4.triangularView<Eigen::Upper>() += ...;
and copy the upper half to the lower afterwards (if needed). This 
however likely reduces vectorization possibilities (try it out, look at 
the generated assembly).
Other than that:
 * What exactly do you mean by homogeneous? Can you make any 
assumptions on the determinant of G? (Calculating the det didn't not 
seem to be the bottleneck, though)
 * Is the same E used for lots of G? Does it have any special form 
(e.g. low rank, or Identity+lowRank)

Christoph

On 2016-02-04 16:17, Alberto Luaces wrote:
> Gael Guennebaud writes:
>
> > Hi,
> >
> > you can avoid one temp with:
> >
> > I4x4.noalias() += ...;
>
> Ok.  Nevertheless, there is no big difference.
>
> > Then slowndown might come from the compiler doing a bad job at
> > inlining. What is your compiler?
>
> gcc version 5.3.1 20160121 (Debian 5.3.1-7)
>
> > version?
>
> libeigen3-dev  3.3~beta1-2
>
> > What are the exact compilation flags?
>
> -msse4 -O3 -DNDEBUG   -std=gnu++11
>
> ...aside from -I preprocessor flags.  "-msse4" seems to make no
> difference either.
>
> > Also, please paste the complete declaration of
> > call_dense_assignment_loop.
>
> Eigen::internal::call_dense_assignment_loop<Eigen::Matrix<double, 4, 4, 0, 4, 4>, Eigen::Product<Eigen::Product<Eigen::Matrix<double, 4, 4, 0, 4, 4>, Eigen::Matrix<double, 4, 4, 0, 4, 4>, 0>, Eigen::Matrix<double, 4, 4, 0, 4, 4>, 1>, Eigen::internal::assign_op<double> >
>
> Thanks!

--
 Dipl. Inf., Dipl. Math. Christoph Hertzberg

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