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? Thomas --------------------------------------------------------------------- To unsubscribe, e-mail: dev-unsubscr...@commons.apache.org For additional commands, e-mail: dev-h...@commons.apache.org
