Re: [eigen] Copy into a MappedSparseMatrix

[Christoph Hertzberg <chtz@xxxxxxxxxxxxxxxxxxxxxxxx>]

On 16.07.2015 at 17:22, Norman Goldstein wrote:
> So,  copy( a, b ) works, but copy( a*b, c ) does not work.

Directly assigning a product to a MappedSparseMatrix won't work, since 
the number of non zeros are not known beforehand, so you need to 
evaluate into a temporary anyways. The reason why your code does not 
automatically convert into a temporary is that implicit type conversions 
are disabled for templated functions.

I still don't understand why you want to assign your result to a Mapped 
matrix?


N.B.: I thought about "recomputing" sparse products (without 
re-allocating) quite a while ago 
(http://eigen.tuxfamily.org/bz/show_bug.cgi?id=284, 
http://eigen.tuxfamily.org/bz/show_bug.cgi?id=385), but never found it 
important enough to further work on that. If someone wants to work on 
that, contributions are welcome.


Christoph



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Dipl.-Inf., Dipl.-Math. Christoph Hertzberg
Cartesium 0.049
Universität Bremen
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