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- To: eigen@xxxxxxxxxxxxxxxxxxx
- Subject: Re: [eigen] Index type for PermutationMatrix and Transpositions
- From: Gael Guennebaud <gael.guennebaud@xxxxxxxxx>
- Date: Tue, 25 Jan 2011 16:14:52 +0100
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On Tue, Jan 25, 2011 at 1:54 PM, Benoit Jacob <jacob.benoit.1@xxxxxxxxx> wrote:
> 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.
The problem is that the index type of Matrix is not really
controllable. Now think about the idea of computing the LU or LDLT
decomposition of a *dense* matrix larger than 2^32 x 2^32 ...
gael
> Benoit
>
>>
>> Christoph
>>
>> --
>> ----------------------------------------------
>> Dipl.-Inf. Christoph Hertzberg
>> Cartesium 0.051
>> Universität Bremen
>> Enrique-Schmidt-Straße 5
>> 28359 Bremen
>>
>> Tel: (+49) 421-218-64252
>> ----------------------------------------------
>>
>>
>>
>
>
>