On Jan 14, 11:27 am, Asbjørn Bjørnstad <asbj...@gmail.com> wrote:
> On Jan 14, 12:20 pm, "Mark H." <mark.hoem...@gmail.com> wrote:
>
>
>
> > I humbly propose that folks shouldn't complain about Clojure being
> > slow for their apps until they have at least one of the following:
>
> > 1. A targeted benchmark for an important bottleneck in their
> > application, implemented in both Clojure and the current
> > implementation language, with performance results; or
>
> > 2. A performance model based on an understanding of the Clojure and
> > HotSpot compilation processes, that highlights which particular
> > features of the latter would make their application slower than in its
> > current implementation language.
>
> > This is not out of elitism but out of an earnest desire to be helpful;
> > it's hard to give good advice on language choice and code optimization
> > when we don't know what the bottlenecks are. Also it's really hard
> > for anyone to optimize their own code unless they themselves know
> > where the bottlenecks are. The latter means that #1 above is
> > surprisingly easy; it often can be done with a simple function trace
> > of a typical run.
>
> I'm not complaining, but I find the topic interesting as I just tried
> translating a fluid dynamics algorithm to clojure.
> (http://www.dgp.toronto.edu/people/stam/reality/Research/pdf/
> GDC03.pdf)
> I got no experience with this kind of stuff, it's just something I
> tried out for fun. So the performance I get may be as expected. Or
> there may be obvious ways of speeding it up that I don't see.
>
> Anyway, here is a core part of the algorithm. It's a diffusion
> step, this gets called 3 times and in total this takes up more than
> one second of cpu time on my machine which makes framerates very
> slow. If anyone got any improvements I'd be happy to hear about it:
>
> (def grid-size 300)
>
> (defn make-grid []
> (make-array Float/TYPE (* (+ grid-size 2)
> (+ grid-size 2))))
>
> (defn diffuse [grid diff-ratio dt]
> (let [a (float (* dt diff-ratio grid-size grid-size))
> a4-1 (float (+ 1 (* 4 a)))
> grid #^floats (deref grid)
> diffused-grid #^floats (make-grid)
> line-length (int (+ grid-size 2))]
> (dotimes [n 20]
> (dotimes [y grid-size]
> (let [line-offset (* (inc y) line-length)]
> (loop [x (int 1)
> c (+ x line-offset)]
> (aset diffused-grid c
> (float (/ (+ (aget grid c)
> (* a
> (+ (+ (aget diffused-grid (dec
> c))
> (aget diffused-grid (inc
> c)))
> (+ (aget diffused-grid (- c
> line-length))
> (aget diffused-grid (+ c
> line-length))))))
> a4-1)))
> (when (< x grid-size)
> (recur (inc x)
> (inc c)))))))
> diffused-grid))
>
> (def foo (ref (make-grid)))
>
> (time (diffuse foo 0.00025 0.002))
>
Try this (and make sure you are using -server):
(defn diffuse [grid diff-ratio dt]
(let [a (float (* dt diff-ratio grid-size grid-size))
a4-1 (float (+ 1 (* 4 a)))
grid #^floats (deref grid)
diffused-grid #^floats (make-grid)
grid-size (int grid-size)
line-length (int (+ grid-size 2))]
(dotimes [n 20]
(dotimes [y grid-size]
(let [line-offset (* (inc y) line-length)]
(loop [x (int 1)
c (int (+ x line-offset))]
(aset diffused-grid c
(/ (+ (aget grid c)
(* a
(+ (+ (aget diffused-grid
(unchecked-dec c))
(aget diffused-grid
(unchecked-inc c)))
(+ (aget diffused-grid
(unchecked-subtract c line-length))
(aget diffused-grid
(unchecked-add c line-length))))))
a4-1))
(when (< x grid-size)
(recur (unchecked-inc x)
(unchecked-inc c)))))))
diffused-grid))
(time (diffuse foo 0.00025 0.002))
"Elapsed time: 25.588 msecs"
Rich
--~--~---------~--~----~------------~-------~--~----~
You received this message because you are subscribed to the Google Groups
"Clojure" group.
To post to this group, send email to clojure@googlegroups.com
To unsubscribe from this group, send email to
clojure+unsubscr...@googlegroups.com
For more options, visit this group at
http://groups.google.com/group/clojure?hl=en
-~----------~----~----~----~------~----~------~--~---
