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#1
March 14th, 2005, 01:35 PM
 wx_uab
Contributing User

Join Date: Jun 2004
Location: Bimingham,AL
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Optimization in C/C++

Dear All,

I have the following function which i am thinking of writing in C/C++ bcos its taking ages to run that in python

Code:
```def calculateCooccurence(self, matrix,intensityList):
coMatrix = zeros((len(intensityList),len(intensityList)))
for i in range(len(intensityList)):
ival = intensityList[i]
for j in range(len(intensityList)):
jval = intensityList[j]
for x in range(len(matrix)-1):
for y in range(len(matrix[0])-1):

if matrix[x][y] ==ival and matrix[x+1][y+1] =jval:
coMatrix[i][j] = coMatrix[i][j]+1```

but inorder to do that i will have to pass a one dimesional and two dimensional list ( intensityList and matrix ) to C function and pass back a two dimensional array (coMatrix).

Can anyone help me with passing arrays back and forth between c and python

#2
March 14th, 2005, 02:20 PM
 netytan
Hello World :)

Join Date: Mar 2003
Location: Hull, UK
Posts: 2,537
Time spent in forums: 1 Week 2 Days 18 h 17 m 47 sec
Reputation Power: 68
You should use the enumerate function for the first two for loops, this will make things easier to read. The function can probably be optimized but I will have to look at that later .

Personally I haven't played around with the CPython API but you can read more on this in the Python docs.

http://www.python.org/doc/2.3.4/ext/ext.html

You may also be interested in the cTypes library, which allows you to call C functions from Python.

http://starship.python.net/crew/theller/ctypes/

There are so many solutions for this kind of thing including Psyco, SWIG, Boost Python, Pyrex etc. I would suggest looking at some of these and seeing which will work best for your situation.

http://psyco.sourceforge.net/
http://www.swig.org/tutorial.html
http://nz.cosc.canterbury.ac.nz/~greg/python/Pyrex/
http://boost.org/libs/python/doc/

Hope this helps,

Mark.
wx_uab agrees!
__________________
programming language development: www.netytan.com Hula

#3
March 14th, 2005, 03:43 PM
 DevCoach
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Location: London, England
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You should also check out Numerical Python and numarray.

They are both high-performance libraries for manipulating matrices.

Dave - The Developers' Coach

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