I got scipy.weave working in my Mandelbrot demo in Python2.5 under Cygwin, and
the speed improvement is comparable to my hand-coded <Pyton.h> extension module.
1a) Python speed = 678 points/sec
1b) C speed = 115200 points/sec 169X
2a) Python speed = 721 points/sec
2b) C speed = 126400 points/sec 175X
See
http://ece.arizona.edu/~edatools/ece175/projects/mandelbrots/mandel_weave.py
for the complete program, including both the Python and C-coded versions of the
getpts function. It should run now in any Python setup with the required
packages (numpy and weave).
As Rob pointed out, this eliminates all the <Python.h> interface functions, the
need to build a shared library for every little test, and the clutter in my
site-packages directory from all these tests. Now, I can just tell the
students "write your own C code, and put it in the stub function in this Python
module."
The stub function runs 10X faster than the C speed above, so we can be
confident the Python overhead is negligible.
At 09:30 PM 3/13/2008 -0700, Rob Malouf wrote:
>Ugh! I'm afraid I don't use windows, so I can't offer any advice. I
>do know that compiling scipy wasn't that difficult under linux or mac
>os x, so it shouldn't be too bad under cygwin either.
Weave and Numpy compiled without any snags, and that is all I need for now.
> There are few
>extra libraries you need, but you can probably find binaries for them
>out there somewhere. In fact, I'm surprised there isn't a cygwin
>binary for scipy... if you get it working maybe you should post it
>somewhere!
Or at least some instructions that are more clear on building such a binary.
Many thanks for all the help.
-- Dave
At 07:24 PM 3/11/2008 -0700, Rob Malouf wrote:
>On Mar 11, 2008, at 5:11 PM, David MacQuigg wrote:
>>It would make a nice improvement in this Mandelbrot demo if you
>>could show me a way to significantly improve the speed of the Python
>>I already have, perhaps avoiding the need for C.
>
>Actually, I don't see a clean way to vectorize that inner loop, so
>maybe numpy isn't a good fit here. Which means weave is.
>
>First, running the program as-is, I get:
>
> 1a) Python speed = 776 points/sec
> 1b) C speed = 103200 points/sec
> 2a) Python speed = 833 points/sec
> 2b) C speed = 108600 points/sec
>
>With this added to the beginning of the program to load and invoke
>psyco:
>
> import psyco
> psyco.full()
>
>I get:
>
> 1a) Python speed = 2700 points/sec
> 1b) C speed = 101600 points/sec
> 2a) Python speed = 2800 points/sec
> 2b) C speed = 110100 points/sec
>
>Or, instead, replacing your getpts with the weave-d version:
>
> from numpy import zeros
> from scipy import weave
> ...
> vals = zeros(100,int)
>
> code = r"""
> double cx = cx0 - dx;
> for (int p=0; p<100; p++) {
> double zx = 0.0;
> double zy = 0.0;
> int i;
> cx += dx;
> for (i=0; i<999; i++) {
> double zx2 = zx*zx;
> double zy2 = zy*zy;
> if ((zx2 + zy2) > 4.0) break;
> zy = 2*zx*zy + cy0;
> zx = zx2 - zy2 + cx;
> }
> vals[p] = i;
> }
> """
> weave.inline(code,['cx0','cy0','dx','vals'])
>
>I get:
>
> 1a) Python speed = 102200 points/sec
> 1b) C speed = 103300 points/sec
> 2a) Python speed = 108400 points/sec
> 2b) C speed = 110700 points/sec
>
>Not bad! There's probably a more pythonic way to write that, but
>this'll do. And after all, this is a realistic situation: you've got
>the inner loop of a program written in C, but you'd rather write all
>the supporting code around it in something like Python. And note that
>weave automatically compiles and links (if necessary) and then loads
>the C part when you run mandel.py. You (or your students) don't need
>to remember where the python headers are or how to build a shared
>library on whatever platform they're using.
>
>---
>Rob Malouf <[EMAIL PROTECTED]>
>Department of Linguistics and Asian/Middle Eastern Languages
>San Diego State University
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