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/** @file time_gammaseries.cpp
*
* Some timings on series expansion of the Gamma function around a pole. */
/*
* GiNaC Copyright (C) 1999-2025 Johannes Gutenberg University Mainz, Germany
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*/
#include "ginac.h"
#include "timer.h"
using namespace GiNaC;
#include <iostream>
#include <vector>
using namespace std;
unsigned tgammaseries(unsigned order)
{
unsigned result = 0;
symbol x;
ex myseries = series(GiNaC::tgamma(x),x==0,order);
// compute the last coefficient numerically:
ex last_coeff = myseries.coeff(x,order-1).evalf();
// compute a bound for that coefficient using a variation of the leading
// term in Stirling's formula:
ex bound = exp(-.57721566490153286*(order-1))/(order-1);
if (abs((last_coeff-pow(-1,ex(order)))/bound) > 1) {
clog << "The " << order-1
<< "th order coefficient in the power series expansion of tgamma(0) was erroneously found to be "
<< last_coeff << ", violating a simple estimate." << endl;
++result;
}
return result;
}
unsigned time_gammaseries()
{
unsigned result = 0;
cout << "timing Laurent series expansion of Gamma function" << flush;
vector<unsigned> sizes = {20, 25, 30, 35};
vector<double> times;
timer omega;
for (vector<unsigned>::iterator i=sizes.begin(); i!=sizes.end(); ++i) {
omega.start();
result += tgammaseries(*i);
times.push_back(omega.read());
cout << '.' << flush;
}
// print the report:
cout << endl << " order: ";
for (vector<unsigned>::iterator i=sizes.begin(); i!=sizes.end(); ++i)
cout << '\t' << *i;
cout << endl << " time/s:";
for (vector<double>::iterator i=times.begin(); i!=times.end(); ++i)
cout << '\t' << *i;
cout << endl;
return result;
}
extern void randomify_symbol_serials();
int main(int argc, char** argv)
{
randomify_symbol_serials();
cout << setprecision(2) << showpoint;
return time_gammaseries();
}
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