Re: [eigen] Matrix multiplication seems to be exceptionally slow in one specific case |

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*To*: eigen@xxxxxxxxxxxxxxxxxxx*Subject*: Re: [eigen] Matrix multiplication seems to be exceptionally slow in one specific case*From*: Christoph Hertzberg <chtz@xxxxxxxxxxxxxxxxxxxxxxxx>*Date*: Mon, 16 Jun 2014 17:54:10 +0200

On 16.06.2014 17:02, Marc Glisse wrote:

On Mon, 16 Jun 2014, Christian Seiler wrote:There has been a proposal for 'operator auto' in C++ because of this, but there doesn't seem to be enough traction for it.The latest related paper is: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2014/n4035.pdf and the committee will discuss it this week. If you have any comments, please feel free to post them on: https://groups.google.com/a/isocpp.org/forum/#!forum/std-proposals There is some resistance to this kind of change, so any extra information (use cases, requirements, suggestions, etc) helps, not least because it shows interest in the proposal.

In some cases it might even degrade performance, e.g.: auto AB = A*B; // shall this evaluate into a temporary? MatrixXd result = AB+C; // actually, no explicit temporary AB required // direct evaluation would have been better What would also be confusing is that passing a product to template<class Matrix> void foo(const Matrix&); will not do automatic 'auto'-conversion, but this would: auto X = expression; // auto-conversion foo(X); // converted X foo(expression); // no conversion

I posted a bug for that: http://eigen.tuxfamily.org/bz/show_bug.cgi?id=825 Christoph -- ---------------------------------------------- Dipl.-Inf., Dipl.-Math. Christoph Hertzberg Cartesium 0.049 Universität Bremen Enrique-Schmidt-Straße 5 28359 Bremen Tel: +49 (421) 218-64252 ----------------------------------------------

**Follow-Ups**:

**References**:**[eigen] Matrix multiplication seems to be exceptionally slow in one specific case***From:*Thijs.Kooi

**Re: [eigen] Matrix multiplication seems to be exceptionally slow in one specific case***From:*Christian Seiler

**Re: [eigen] Matrix multiplication seems to be exceptionally slow in one specific case***From:*Marc Glisse

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