bmaxa <at> maxa:~/haskell$ time ./createMatrixDump.py -N 128 > output.txt

real 0m0.041s

user 0m0.040s

sys 0m0.000s

bmaxa <at> maxa:~/haskell$ time ./printMatrixDecay.py - < output.txt

(-) read 16384 matrix elements (128x128 = 16384)

[0.00e+00, 1.00e-08) = 0 (0.00%) 0

[1.00e-08, 1.00e-07) = 0 (0.00%) 0

[1.00e-07, 1.00e-06) = 0 (0.00%) 0

[1.00e-06, 1.00e-05) = 0 (0.00%) 0

[1.00e-05, 1.00e-04) = 1 (0.00%) 1

[1.00e-04, 1.00e-03) = 15 (0.00%) 16

[1.00e-03, 1.00e-02) = 149 (0.00%) 165

[1.00e-02, 1.00e-01) = 1425 (0.00%) 1590

[1.00e-01, 1.00e+00) = 14794 (0.00%) 16384

[1.00e+00, 2.00e+00) = 0 (0.00%) 16384

real 0m0.081s

user 0m0.072s

sys 0m0.008s

bmaxa <at> maxa:~/haskell$ time ./printMatrixDecay < output.txt

read 16384 matrix elements (128x128 = 16384)

[0.00e+00, 1.00e-08) = 0 (0.00%) 0

[1.00e-08, 1.00e-07) = 0 (0.00%) 0

[1.00e-07, 1.00e-06) = 0 (0.00%) 0

[1.00e-06, 1.00e-05) = 0 (0.00%) 0

[1.00e-05, 1.00e-04) = 1 (0.01%) 1

[1.00e-04, 1.00e-03) = 15 (0.09%) 16

[1.00e-03, 1.00e-02) = 149 (0.91%) 165

[1.00e-02, 1.00e-01) = 1425 (8.70%) 1590

[1.00e-01, 1.00e+00) = 14794 (90.30%) 16384

[1.00e+00, 2.00e+00) = 0 (0.00%) 16384

real 0m0.018s

user 0m0.012s

sys 0m0.004s

unfortunately g++ does not have regex implemented yet so I used libpcre ...

#include <pcre.h>

#include <sstream>

#include <cstdio>

#include <cmath>

#include <iostream>

#include <stdexcept>

#include <vector>

template <class F>

void regex(const std::string& in, const std::string& pattern,int n,F f)

{

int ovec[3*n],position;

const char* error;

int errorpos;

pcre* pe = pcre_compile(pattern.c_str(),0,&error,&errorpos,0);

if(!pe)throw std::runtime_error(error);

pcre_extra* extra=pcre_study(pe,0,&error);

for(position = 0;

pcre_exec(pe,extra,in.c_str(),in.size(),position,0,ovec,3*n)>=0;

position = ovec[1])f(position,ovec);

f(position,ovec);

pcre_free(extra);

pcre_free(pe);

}

int main()

{

std::ios::sync_with_stdio(false);

std::ostringstream oss;

oss << std::cin.rdbuf();

const std::string& in = oss.str();

std::vector<double> strataBounds = { 0.0, 1.0e-8, 1.0e-7, 1.0e-6, 1.0e-5, 1.0e-4, 1.0e-3, 1.0e-2, 1.0e-1, 1.0, 2.0 };

std::vector<int> strataCounts(strataBounds.size());

unsigned N = 0;

auto f = [&](int position,int* ovec)

{

if(int(position) > ovec[0])return;

++N;

double aij = 0.0;

std::istringstream iss(in.substr(ovec[2],ovec[3]-ovec[2]));

iss >> aij;

aij=fabs(aij);

for(unsigned i = 0; i < strataBounds.size() - 1; ++i)

{

if(aij >= strataBounds[i] && aij < strataBounds[i+1])

{

++strataCounts[i];

break;

}

}

};

regex(in,"matrix.*= ([0-9.eE+-]+)\n",2,f);

printf("read %d matrix elements (%dx%d = %d)\n",N,int(sqrt(N)),int(sqrt(N)),N);

int total = 0;

for(unsigned i = 0; i< strataBounds.size()-1;++i)

{

total += strataCounts[i];

printf("[%1.2e, %1.2e) = %d (%1.2f%%) %d\n", strataBounds[i], strataBounds[i+1],

strataCounts[i], 100*(double(strataCounts[i])/N), total);

}

}

From: nicolasbock <at> gmail.com

Date: Fri, 8 Feb 2013 12:26:09 -0700

To: haskell-cafe <at> haskell.org

Subject: [Haskell-cafe] performance question

Hi list,

I wrote a script that reads matrix elements from standard input, parses the input using a regular expression, and then bins the matrix elements by magnitude. I wrote the same script in python (just to be sure :) ) and find that the python version vastly outperforms the Haskell script.

To be concrete:

$ time ./createMatrixDump.py -N 128 | ./printMatrixDecay

real 0m2.655s

user 0m2.677s

sys 0m0.095s

$ time ./createMatrixDump.py -N 128 | ./printMatrixDecay.py -

real 0m0.445s

user 0m0.615s

sys 0m0.032s

The Haskell script was compiled with "ghc --make printMatrixDecay.hs".

Could you have a look at the script and give me some pointers as to where I could improve it, both in terms of performance and also generally, as I am very new to Haskell.

Thanks already,

nick

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