| Re: [eigen] what do you think of this simple benchmark |
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- To: eigen@xxxxxxxxxxxxxxxxxxx
- Subject: Re: [eigen] what do you think of this simple benchmark
- From: "Benoit Jacob" <jacob.benoit.1@xxxxxxxxx>
- Date: Sun, 4 Jan 2009 18:45:35 +0100
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2009/1/4 Matthias Pospiech <matthias.pospiech@xxxxxx>:
> The simple matrix class can be seen here:
> http://www.c-plusplus.de/forum/viewtopic-var-t-is-230960.html
> (comments welcome).
Your matrix is stored as a vector<vector>. That's not optimal. For
example, since each vector needs to store its size, the size is
getting stored n times for a n*n matrix... With a good STL
implementation, for large sizes, it may be asymptotically as fast as a
plain C array (like Eigen uses) but for small sizes you're going to
get a big overhead.
Your matrix is dynamic-size (as std::vector is, i.e. size is a runtime
variable), but in your benchmark below you compare it against Eigen's
fixed-size Matrix4f. Fixed-size matrices go much faster than dynamic
size ones...
Other than that, nothing special to say... remember to use gcc 4.2 or
newer -O2 -DNDEBUG for benchmarking Eigen, that's all.
Cheers,
Benoit
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