On Sunday, November 6, 2016 at 2:25:27 AM UTC-8, Milan Bouchet-Valat wrote: > > For reference, here's the long discussion that happened before making > that change: > https://github.com/JuliaLang/julia/pull/16371 > > Indeed I think Tony was right that this has undesirable consequences in > terms of usability. Not being able to use the same in-place API for > dense and sparse matrices is a no-go IMHO. > > Please elaborate. You cannot resize dense matrices in-place either.
Just create a new matrix from the fields of the old one if you want to change the size. How does this limit usability? > > Regards > > Le samedi 05 novembre 2016 à 20:11 -0700, vav...@uwaterloo.ca > <javascript:> a > écrit : > > Just to clarify, you don't actually need to allocate the memory for > > two large sparse matrices. You can change colptr, rowval, and nzval > > in place (as you have already done) and then create a new sparse > > matrix using these modified arrays. In this case, the arrays won't > > be copied over; instead the new sparse matrix will get a pointer to > > the already-allocated arrays. This technique could lead to some > > subtle program bugs (because if two sparse matrices share an nzval > > array, then any change to one affects the other), but you can guard > > against this by making the old matrix's name inaccessible, for > > instance, by giving the new matrix the same name as the old one. > > > > -- Steve Vavasis > > > > > > > I see. returning a new, smaller instance of the matrix was my > > > temporary solution. Bummer that it's necessary... Is it really so > > > strange to want to change the size of a > > > > > > Another alternative which occurs to me is to make some child class > > > of SparseCSCMatrix with two more arrays, each with one element, > > > which track the sizes? Since I am making the matrix smaller, not > > > larger, I can't imagine that this would be an issue. However, if I > > > need to allocate two large sparse matrices just to remove a row/col > > > pair, then I can suddenly use half the memory I could before... > > > > > > > > > > When a type is immutable, that means you can't modify the data in > > > > the type. If a field of a type is mutable, a reference to it is > > > > stored in the type, and you cannot modify that reference. In the > > > > case of SparseMatrixCSC, that means you can't make A.colptr point > > > > to a different array, for example. You are still free to change > > > > the values in A.colptr, because that does not require modifying > > > > the reference. If the field is immutable, then the value itself > > > > is stored in the type, not a reference to the value, and you > > > > cannot modify the value. That's why you get the error in the > > > > example. > > > > > > > > The best solution I can think of for your rmCol example is to > > > > create a new SparseMatrixCSC that uses the same arrays as the old > > > > one (to avoid increasing memory usage) and return it. Replacing > > > > the last line of rmCol with: > > > > > > > > SparseMatrixCSC(m, n-1, A.colptr, A.rowval, A.nzval) > > > > > > > > should do the trick. The only sticky point is that the > > > > original A now contains invalid data, so you'll have to make sure > > > > only the the matrix returned from rmCol is used in the future, > > > > not the original A. > > > > > > > > Jared Crean > > > > > > > > > > > > > The SparseMatrixCSC type is immutable, which I understand to > > > > > mean that I must respect the types of the attributes of > > > > > SparseMatrixCSC types, as well as not changing the attributes > > > > > themselves. > > > > > > > > > > The following gives a loadError (type is immutable). I am > > > > > confused that I can modify the colptr and rowval attributes of > > > > > A, but not the A.n attribute. Why is this? I am trying to > > > > > change the size of a sparse matrix after removing the data from > > > > > a row and column. > > > > > > > > > > I have checked that both A.n and A.n - 1 are type Int. > > > > > > > > > > function rmCol(A::SparseMatrixCSC, rmCol::Int) > > > > > colRmRange = A.colptr[rmCol]:(A.colptr[rmCol+1]-1) > > > > > filter!(e -> e != rmCol, A.colptr) > > > > > > > > > > deleteat!(A.rowval, rowval[colRmRange]) > > > > > deleteat!(A.nzval, colRmRange) > > > > > A.n -= 1 # inclusion of this line throws error > > > > > > > > > > end > > > > > > > > > > > > >
