Matt J
Posts:
4,997
Registered:
11/28/09


Re: speeding up ACCUMARRAY
Posted:
Nov 14, 2012 12:40 PM


"Matt J" wrote in message <k80bi9$isp$1@newscl01ah.mathworks.com>... > "Bruno Luong" <b.luong@fogale.findmycountry> wrote in message <k7vfli$da4$1@newscl01ah.mathworks.com>... > > "Matt J" wrote in message <k7ulhl$iod$1@newscl01ah.mathworks.com>... > > > > >In fact, the sparse matrix multiplication is probably even handicapped relative to accumarray, since it has to search through x for the appropriate x(J), > > > > There is no such step in sparse multiplication. > ============= > > Meaning that y=A*x is generated by looping over columns of A instead of rows? Even if so, how would that explain the speed difference? ================
Anyway, my point remains. Sparse matrix multiplication has to perform multiplications with the x(j) somewhere, whereas accumarray, in my tests, does not. So sparse mult. is further handicapped.

