I posted this few weeks ago (remember the C Sharp thread?) but it went

unnoticed on the large mass of posts, so let me retry. Here I get Python+

Psyco twice as fast as optimized C, so I would like to now if something

is wrong on my old laptop and if anybody can reproduce my results.

Here are I my numbers for calling the error function a million times

(Python 2.3, Psyco 1.0, Red Hat Linux 7.3, Pentium II 366 MHz):

$ time p23 erf.py

real 0m0.614s

user 0m0.551s

sys 0m0.029s

This is twice as fast as optimized C:

$ gcc erf.c -lm -o3

$ time ./a.out

real 0m1.125s

user 0m1.086s

sys 0m0.006s

Here is the situation for pure Python

$time p23 erf.jy

real 0m25.761s

user 0m25.012s

sys 0m0.049s

and, just for fun, here is Jython performance:

$ time jython erf.jy

real 0m42.979s

user 0m41.430s

sys 0m0.361s

The source code follows (copied from Alex Martelli's post):

----------------------------------------------------------------------

$ cat erf.py

import math

import psyco

psyco.full()

def erfc(x):

exp = math.exp

p = 0.3275911

a1 = 0.254829592

a2 = -0.284496736

a3 = 1.421413741

a4 = -1.453152027

a5 = 1.061405429

t = 1.0 / (1.0 + p*x)

erfcx = ( (a1 + (a2 + (a3 +

(a4 + a5*t)*t)*t)*t)*t ) * exp(-x*x)

return erfcx

def main():

erg = 0.0

for i in xrange(1000000):

erg += erfc(0.456)

if __name__ == '__main__':

main()

--------------------------------------------------------------------------

# python/jython version = same without "import psyco; psyco.full()"

--------------------------------------------------------------------------

$cat erf.c

#include <stdio.h>

#include <math.h>

double erfc( double x )

{

double p, a1, a2, a3, a4, a5;

double t, erfcx;

p = 0.3275911;

a1 = 0.254829592;

a2 = -0.284496736;

a3 = 1.421413741;

a4 = -1.453152027;

a5 = 1.061405429;

t = 1.0 / (1.0 + p*x);

erfcx = ( (a1 + (a2 + (a3 +

(a4 + a5*t)*t)*t)*t)*t ) * exp(-x*x);

return erfcx;

}

int main()

{

double erg=0.0;

int i;

for(i=0; i<1000000; i++)

{

erg = erg + erfc(0.456);

}

return 0;

}

Michele Simionato, Ph. D.

MicheleSimionato at libero.it

http://www.phyast.pitt.edu/~micheles

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