Le 08/11/2013 18:38, Thomas Neidhart a écrit : > On 10/13/2013 09:41 AM, Ted Dunning wrote: >> Commons math decided not to support sparse matrices due to the difficulty >> of getting them just right. >> >> The problem is that 0 * Inf = NaN, not 0. This means that for floating >> point math, 0 * x = x is not a true identity. >> >> The problem really arises when the 0 in question could be either stored as >> a 0 or not. Not storing zeros is, of course, the hallmark and calling card >> of sparse matrices because if you assume that the zero multiplication >> identity holds, you can avoid lots of arithmetic. >> >> Unfortunately, if the other matrix or vector has Inf in it, multiplying by >> a sparse matrix where the corresponding element is missing gives a 0 >> instead of NaN. Moreover, the dot product gives a value instead of NaN. >> >> This is very hard to fix and still retain the desirable speed properties of >> sparse matrices. You could imagine that you have a bitmap of all of the >> Inf values in every matrix, but keeping that bitmap up to date can >> absolutely kill performance since you have the potential for a branch in >> critical inner loops. >> >> Most sparse matrices just punt and say they are sorry in a very >> non-IEEE-754 sort of way. >> >> Commons Math has decided instead to remove sparse matrices entirely. > > is there still consensus that we are going to remove the sparse > implementations with 4.0?
Well, I really think it is a pity, we should support this. But lets face it: up to now we have been unable to do it properly. Sébastien who tried to do something in this direction has left the project and nobody replaced him. Luc > > Thomas > > --------------------------------------------------------------------- > To unsubscribe, e-mail: dev-unsubscr...@commons.apache.org > For additional commands, e-mail: dev-h...@commons.apache.org > > > --------------------------------------------------------------------- To unsubscribe, e-mail: dev-unsubscr...@commons.apache.org For additional commands, e-mail: dev-h...@commons.apache.org
