Who said force? Linear algebra operations should be available. Visitors should be available.
Your mileage will vary. That was always true. On Sat, Dec 29, 2012 at 3:59 PM, Konstantin Berlin <kber...@gmail.com>wrote: > Also. If you have GPU implementation of a matrix, or use another type of a > vector processor, there is no way you can program that in if you force > vector operations to use a visitor patterns. > > On Dec 29, 2012, at 6:43 PM, Konstantin Berlin <kber...@gmail.com> wrote: > > > That's a good point about the compiler. I never tested the performance > of visitors vs. sequential array access. I just don't want the vector > operations to be tied to any particular implementation detail. > > > > On Dec 29, 2012, at 6:30 PM, Ted Dunning <ted.dunn...@gmail.com> wrote: > > > >> Actually, the visitor pattern or variants thereof can produce very > >> performant linear algebra implementations. You can't usually get quite > >> down to optimized BLAS performance, but you get pretty darned fast code. > >> > >> The reason is that the visitor is typically a very simple class which is > >> immediately inlined by the JIT. Then it is subject to all of the normal > >> optimizations exactly as if the code were written as a single concrete > >> loop. For many implementations, the bounds checks will be hoisted out > of > >> the loop so you get pretty decent code. > >> > >> More importantly in many cases, visitors allow in place algorithms. > >> Combined with view operators that limit visibility to part of a matrix, > >> and the inlining phenomenon mentioned above, this can have enormous > >> implications to performance. > >> > >> A great case in point is the Mahout math library. With no special > efforts > >> taken and using the visitor style fairly ubiquitously, I can get about > 2 G > >> flops from my laptop. Using Atlas as a LINPAK implementation gives me > >> about 5 G flops. > >> > >> I agree with the point that linear algebra operators should be used > where > >> possible, but that just isn't feasible for lots of operations in real > >> applications. Getting solid performance with simple code in those > >> applications is a real virtue. > >> > >> On Sat, Dec 29, 2012 at 3:22 PM, Konstantin Berlin <kber...@gmail.com > >wrote: > >> > >>> While visitor pattern is a good abstraction, I think it would make for > >>> terrible linear algebra performance. All operations should be based on > >>> basic vector operations, which internally can take advantage of > sequential > >>> memory access. For large problems it makes a difference. The visitor > >>> pattern is a nice add on, but it should not be the engine driving the > >>> package under the hood, in my opinion. > >>> > > > > > --------------------------------------------------------------------- > To unsubscribe, e-mail: dev-unsubscr...@commons.apache.org > For additional commands, e-mail: dev-h...@commons.apache.org > >
