Re: [eigen] Index type for PermutationMatrix and Transpositions |

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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 10:18:37 -0500*Dkim-signature*: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:mime-version:in-reply-to:references:date :message-id:subject:from:to:content-type:content-transfer-encoding; bh=aYhglpqGIet703vLwm9O2nHEmvHei0M6y7lO65bC9Q0=; b=POgW8AhTGIH89llAL+waC44fgSbRZ62GNBM9i+2yeswgvfLi0PtNCJwoKjrXq+XBAP PjfUHT2tU4QPNrnQI7g8KrVHhDUwNUCr67Yqr9zJPC20qwliYqV5XBnW9C4/mme+dUfx Yz2SSzDRiEgv3AOXsQEGnUn60ljRsPQmEApok=*Domainkey-signature*: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :content-type:content-transfer-encoding; b=qxhKDN+PmRDEMg5QlDvZBoUkucrbqOOnuO8kQ6Hv3857hS7E8E3WlEgtnw9gnf3Bab bgyGfqBtmsAvR4SsxPj+VXNRdFj1qK0l/13XR6P8Vdvy4FdjW8Eyp3alG+fVS6AiQF4b dE9xkkocF8M676KoRLp1A0fnYFWK+lfIfB9y8=

2011/1/25 Gael Guennebaud <gael.guennebaud@xxxxxxxxx>: > 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. What do you mean? The user who is ready to break the ABI can control the default index type for dense objects by defining EIGEN_DEFAULT_DENSE_INDEX_TYPE. >Now think about the idea of computing the LU or LDLT > decomposition of a *dense* matrix larger than 2^32 x 2^32 ... Not sure that I follow :) you would need a very big computer, and the result would be 42 anyway :) Benoit > > > gael > > >> Benoit >> >>> >>> Christoph >>> >>> -- >>> ---------------------------------------------- >>> Dipl.-Inf. Christoph Hertzberg >>> Cartesium 0.051 >>> Universität Bremen >>> Enrique-Schmidt-Straße 5 >>> 28359 Bremen >>> >>> Tel: (+49) 421-218-64252 >>> ---------------------------------------------- >>> >>> >>> >> >> >> > > >

**References**:**Re: [eigen] Index type for PermutationMatrix and Transpositions***From:*Helmut Jarausch

**Re: [eigen] Index type for PermutationMatrix and Transpositions***From:*Christoph Hertzberg

**Re: [eigen] Index type for PermutationMatrix and Transpositions***From:*Benoit Jacob

**Re: [eigen] Index type for PermutationMatrix and Transpositions***From:*Gael Guennebaud

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