[Numpy-discussion] ising model: f2py vs cython comparison

[Ondrej Certik]

Hi,

I need to write 2D Ising model simulation into my school, so I wrote
it in Python, then rewrote it in Fortran + f2py, and also Cython:

http://hg.sharesource.org/isingmodel/

And Cython solution is 2x faster than f2py. I understand, that I am
comparing many things - wrappers, my fortran coding skills
vs Cython C code generation and gcc vs gfortran. But still any ideas
how to speed up fortran+f2py solution is very welcomed.

How to play with that - just do this (after installing Mercurial):

$ hg clone http://hg.sharesource.org/isingmodel/
[...]
$ hg up db7dd01cdc26                                 # just to be sure
that we are talking about the same revision / code
$ cd isingmodel
$ make
[...]
$ time python simulate.py
[...]
real	0m2.026s
user	0m1.988s
sys	0m0.020s

This runs Cython code. Then apply this patch to run fortran code instead:

$ hg di
diff -r db7dd01cdc26 simulate.py
--- a/simulate.py	Sun Dec 23 02:23:30 2007 +0100
+++ b/simulate.py	Sun Dec 23 02:24:33 2007 +0100
@@ -31,8 +31,8 @@ def MC(mu = 1, temp = 2, dim = 20, steps
     J=1 #coupling constant
     k=1 #Boltzman constant

-    #from mcising import mc
-    from pyising import mc
+    from mcising import mc
+    #from pyising import mc
     B = D1(A)
     mc(B, dim, steps, temp, H, mu, J, k)
     return D2(B)


And then again:

$ time python simulate.py
[...]
real	0m3.600s
user	0m3.528s
sys	0m0.052s



So it's a lot slower.

Maybe I did some stupid mistake, like doing different amount of steps
in Cython and Fortran, but I tried to check that and if I did
everything all right, it's interesting to find why is fortran+f2py
slower.

Ondrej