Thank you so much for your help! First I defined the size of matrix by i,.j - everything works just fine.
But an idea occured to my mind... Maybe I am not at the right point when using the matrix formulation when solving my task? If you: a) sort the table T(i, j, v) by i value; b) find the beginning and the end of the ranges for each unique value i (let's call them u); c) create a loop by u, and pull the necessary ranges with j and v from the T table; d) apply necessary calculations to the data which are pulled from the other places by j value. Suppose in case we arrange the things this way - this will not be much slower than the matrix formulation method, am I right? Cheers. > a. Currently, mapped files do not support the sparse datatypes. > > b. You can do this in one of two ways: > s=: 1 $. 1e8 1e8 ; 0 1;-~0.5 > s=: value (<"1 i,.j)}s > Or > s=: 1 $. 1e8 1e8 ; 0 1; (-~0.5) ; (i,.j) ; value > (The latter is not yet documented but should work in > J602 beta.) > > A sparse matrix can be converted to the equivalent dense > matrix by d=: $.^:_1 s . > > Note that with your full problem, a 1e8 1e8 matrix with 10e9 > non-zero atoms, there is no advantage to making it a sparse > matrix, because as stated before the primitive %. and > +/ .* are not up to dealing with an array of that size. > Better to just map i and j and values separately > (perhaps i,.j and value as two map files), and apply your > iterative methods to these. > > Perhaps I should add the problem you described is a > non-trivial application. > > > > ----- Original Message ----- > From: Nick Kostirya <[EMAIL PROTECTED]> > Date: Wednesday, January 9, 2008 23:04 > Subject: [Jgeneral] table (i,j,value) to matrix > To: [email protected] > > > Hello, > > > > I proceed with my studies of J, well I have a couple of > > questions for > > you. > > > > As far as I understand, а sparse matrix can't mapped as file, am > > I right? > > > > Second, what's the most optimal way of converting a table > > (i,j,value) into matrix, preferably a sparse one? Can't really get > > the clue... I am also interested in the process of reverse > > conversion... > ---------------------------------------------------------------------- > For information about J forums see http://www.jsoftware.com/forums.htm > ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm
