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*From*: Patrick Alken <alken at colorado dot edu>*To*: Alexis Tantet <alexis dot tantet at gmail dot com>*Cc*: "gsl-discuss at sourceware dot org" <gsl-discuss at sourceware dot org>*Date*: Sun, 7 Feb 2016 14:34:20 -0700*Subject*: Re: Sparse matrix extension*Authentication-results*: sourceware.org; auth=none*Authentication-results*: sourceware.org; dkim=none (message not signed) header.d=none;sourceware.org; dmarc=none action=none header.from=colorado.edu;*References*: <CAMWWPT3uJj4Vrn7ut6+F18gY===zd6+1r1UJhz0hcCj--zwtdg at mail dot gmail dot com> <CAMWWPT3Y=x-vYphaV+2gHPb9WZqEfYdDxs4T0KqBq987VjvDQA at mail dot gmail dot com> <569E6C33 dot 1090505 at colorado dot edu> <CAMWWPT2kMe=R0qUz4P6n_xzG+oW-8pOFwCtBuaritZ5MF6jzAg at mail dot gmail dot com> <569EA1A9 dot 2080101 at colorado dot edu> <CAMWWPT2d=PnK1cexcZ+OLQAYJudRk9QLGac-Wcn33OaES5UjJA at mail dot gmail dot com> <56B689B1 dot 5090005 at colorado dot edu> <CAMWWPT1mog0HrviL1tMo=f-rrSc2PhamWDGg7ZYLrVnnqkY3ng at mail dot gmail dot com> <56B77E13 dot 1000306 at colorado dot edu> <CAMWWPT2KTLjufNdwW=y-xaJ1dKkxDNQwgat4DB4ZwKDrK_fZSA at mail dot gmail dot com> <56B7A59D dot 5040707 at colorado dot edu> <CAMWWPT0CX+ti2j6QM8YmHqv+n8yg7sK69dtSdzKOQMFx3pXeBA at mail dot gmail dot com>*Spamdiagnosticmetadata*: NSPM*Spamdiagnosticoutput*: 1:23

By design, gsl_spmatrix_set won't allow you to do this. If you add element (i, j, x) and then later to try add element (i, j, y), gsl_spmatrix_set will detect that there exists an element in the (i, j) spot and it will simply change x to y - the value of x will be overwritten by y. This is the same behavior as gsl_matrix_set. So no duplicates are allowed by design. If you have such an application where you want to keep track of duplicates, you could do the following: double *ptr = gsl_spmatrix_ptr(m, i, j); if (ptr) *ptr += x; /* sum duplicate values */ else gsl_spmatrix_set(m, i, j, x); /* initalize to x */ On 02/07/2016 01:31 PM, Alexis Tantet wrote: > I'm not sure I got your last point. I have the following situation in mind: > > Start to construct a transition matrix in triplet format, adding one > element after another. > In this particular example, each element is one count of a transition > from (state, box, etc.) i to j, > so I add elements (i, j, 1) to the triplet object, with possibly duplicates. > What happen to these duplicates in the binary tree? > > Eventually, when I compress to CRS or CCS, I would like the duplicates > to be summed up, so that element (i, j) counts transitions from i to j > (and no duplicates exist after compression). > > Is this more clear? > > On Sun, Feb 7, 2016 at 9:14 PM, Patrick Alken <alken@colorado.edu> wrote: >> Hi Alexis, >> >>>> I'm not sure what you mean. I've added a new function gsl_spmatrix_ptr >>>> to the git, which as far as I can tell does exactly what your >>>> sum_duplicate flag does. It searches the matrix for an (i,j) element, >>>> and if found returns a pointer. If not found a null pointer is returned. >>>> This makes it easy for the user to modify A(i,j) after it has been added >>>> to the matrix. Are you thinking of something else? Can you point me to >>>> the Eigen routine? >>>> >>> What I meant is to have the equivalent of gsl_spmatrix_compress, >>> with the difference that gsl_spmatrix_ptr is used instead of gsl_spmatrix_set, >>> so has to build the compressed matrix from triplets, summing the >>> duplicates, instead of replacing them. >>> This is what is done here : >>> The http://eigen.tuxfamily.org/dox/classEigen_1_1SparseMatrix.html#a5bcf3187e372ff7cea1e8f61152ae49b >>> >>> Best, >>> Alexis >> I'm not sure why a user would ever need to do this. The whole point of >> the binary tree structure in the triplet storage is to efficiently find >> duplicate entries, so that if a user tries to call gsl_spmatrix_set on >> an element which is already been previously set, it can find that >> element with a binary search (rather than linearly searching the arrays) >> and change the value of that element. >> >> Therefore, the way the triplet storage is designed, there is will never >> be a duplicate element in the triplet arrays. All of the (i[n],j[n]) >> will be unique for each n <= nz. >> >> Am I missing something? >> >> Patrick > >

**Follow-Ups**:**Re: Sparse matrix extension***From:*Alexis Tantet

**References**:**Re: Sparse matrix extension***From:*Alexis Tantet

**Re: Sparse matrix extension***From:*Patrick Alken

**Re: Sparse matrix extension***From:*Alexis Tantet

**Re: Sparse matrix extension***From:*Patrick Alken

**Re: Sparse matrix extension***From:*Alexis Tantet

**Re: Sparse matrix extension***From:*Patrick Alken

**Re: Sparse matrix extension***From:*Alexis Tantet

**Re: Sparse matrix extension***From:*Patrick Alken

**Re: Sparse matrix extension***From:*Alexis Tantet

**Re: Sparse matrix extension***From:*Patrick Alken

**Re: Sparse matrix extension***From:*Alexis Tantet

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