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- To: eigen@xxxxxxxxxxxxxxxxxxx
- Subject: Re: [eigen] sdgfdf
- From: Gael Guennebaud <gael.guennebaud@xxxxxxxxx>
- Date: Mon, 2 Feb 2009 14:34:40 +0100
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On Mon, Feb 2, 2009 at 2:08 PM, Jens Mueller <jens.k.mueller@xxxxxx> wrote:
> Hi,
>
>> yes this is something I've thought about, there is no difficulty.
>> Actually my initial concern was rather about "int" which could be too
>> small if n > 2^32, so I'll make the types of both "index pointers" and
>> "coordinate" template parameters. Note that with "unsigned short" for
>> the coordinate type, you are limited to 65k x 65k matrices, that is
>> not very large.
>
> Can't I have different types for each coordinate index, i.e. short for
> columns and int for rows? Don't know, if I'm getting your unsigned short
> example right. In my case, only one coordinate index fits into unsigned
> short. The other one should be int.
right, the compressed storage is not symmetric, so if you have a
col-major matrix you could use int for the column index and short for
the row index but not the other way round. Eventually, I think that's
probably a lot of trouble for minor benefits:
- this would complexify operators (matrix product, transposition,
submatrices, etc.),
- the memory gain would be x0.75 for float and x0.83 for double only,
- honestly, I don't expect any performance improvement,
- I don't think other libs are able to handle short type for indices,
so you would not be able to use your matrix with the solvers.
gael.