Ok, my mistake, now I see where I got confused. I had in mind to add all the elements first to the triplets and only while converting to compressed sum up the duplicates. While, indeed, if there's a way you can sum up the duplicates directly while adding them to the triplet matrix (thanks to _ptr), this is more handy and efficient.
Thanks for the clarification, Alexis On Sun, Feb 7, 2016 at 10:34 PM, Patrick Alken <[email protected]> wrote: > 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 <[email protected]> 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 >> >> > -- Alexis Tantet
