[eigen] adding constructor to SparseMatrix |

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*To*: eigen <eigen@xxxxxxxxxxxxxxxxxxx>*Subject*: [eigen] adding constructor to SparseMatrix*From*: Daniel Lowengrub <lowdanie@xxxxxxxxx>*Date*: Mon, 7 Jun 2010 01:11:28 +0300*Cc*: Gael Guennebaud <gael.guennebaud@xxxxxxxxx>*Dkim-signature*: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:mime-version:received:received:date:message-id :subject:from:to:cc:content-type; bh=H1hDbKqW2OAmxMADfGqD53P9kcHiuaGNKelCW9JjjWE=; b=HWuzQ/zgiBJTOeUZh6H2p4eG1CqxA9Rw0b0JE53n/2mLAaKQ1BXdFFNuoOKeFFM0gN 20ZvK6CIM7aBs5gc+oN251wi+i9nc6iDQZT3ECQG5J4SML7sRW/il8999CUpaX8qJZVW /8Z5b4xxYUwZcEQ+omE0k+0txBdQKRcWpMnPw=*Domainkey-signature*: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:date:message-id:subject:from:to:cc:content-type; b=SMOtdQcSSNI07/H88kcx41KbNEHqGwXAIPFuaLwa58Ex1c+oZWnCmb9/5KxosK5zV7 HyjjSCMED3TBo+u0m/Eiv2wygMAV4GGXMfPvajVBEJrpw1/RQ2MJG3h8Cw7ZtZ/+cO/U EoEAtY+6kbZDFcuSt61Zk+59094RPb0n0fqZA=

Sorry about the previous mis-post. I think that it'd be useful to be able to quickly cast a regular Matrix type into a SparseMatrix. I have two questions about the implementation: 1) Would it be better to implement a new SparseMatrix ctor that accepts a Matrix as an argument, or to implement a function like sparseView in the Matrix class which returns a SparseMatrix? 2) At what level would it make sense for this to work? In the first direction, a general MatrixBase shouldn't be able to be turned into a SparseMatrix because this doesn't make sense for some subtypes of MatrixBases such as expressions. In the other direction, if the answer to the first question is to add a ctor, then should it be added to SparseMatrixBase and be available to all of it's children, or should it be specific to SparseMatrix? Casting a DenseMatrix to a SparseMatrix is probably most useful when a DenseMatrix is constructed as part of an algorithm but the algorithm requires operations like factorization and linear system solving which are more efficient when performed on a SparseMatrix [if the matrix is truly sparse]. Because of this, casting a Matrix to a DynamicSparseMatrix doesn't seem too helpful. What do you think? Daniel On 6/7/10, Daniel Lowengrub <lowdanie@xxxxxxxxx> wrote: > >

**Follow-Ups**:**Re: [eigen] adding constructor to SparseMatrix***From:*Gael Guennebaud

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