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- To: eigen@xxxxxxxxxxxxxxxxxxx
- Subject: Re: [eigen] Index type for PermutationMatrix and Transpositions
- From: Benoit Jacob <jacob.benoit.1@xxxxxxxxx>
- Date: Tue, 25 Jan 2011 07:54:46 -0500
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2011/1/25 Christoph Hertzberg <chtz@xxxxxxxxxxxxxxxxxxxxxxxx>:
> On 25.01.2011 10:29, Helmut Jarausch wrote:
>> On 01/25/11 10:11:22, Gael Guennebaud wrote:
>>> Since it is unbelievable
>>> that one day someone will perform a LU or LDLT dec on a matrix
>>> requiring 64bits integers for the indices (think about the size of
>>> the
>>> matrix!), I think it is safe to use int there too.
>
> Just like 640k ought to be enough for everyone ;)
>
>> I agree for dense matrices, but a tridiagonal matrix of size 2^32
>> isn't out of range (IMHO). So the situation might be different for
>> sparse matrices - even in the near future.
>
> I agree on that. Why not make it default to MatrixType::Index and tell
> users to use an appropriate IndexType in the first place? This could be
> even smaller if the matrix never reaches sizes above 2^16 (2^15?).
I agree with Christian here. DenseIndex is the most sane defaut, and
let the user specify smaller integer types.
The problem with defaulting to int is that it is neither what dense
matrices use, nor the smallest integer type.
Benoit
>
> Christoph
>
> --
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> Dipl.-Inf. Christoph Hertzberg
> Cartesium 0.051
> Universität Bremen
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