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#include <iostream>
#ifdef IN_GINAC
#include "ginac.h"
#else
#include <ginac/ginac.h>
#endif
// Yes, we are using CUBA (should be installed on the system!)
#include <cuba.h>
using namespace std;
using namespace GiNaC;
/*
* Demonstrates the use of compile_ex with the CUBA library.
*
* The user can enter an expression on the command line. This expression is
* compiled via compile_ex and integrated over the region 0 <= x,y <= 1 with
* the help of the CUBA library (http://www.feynarts.de/cuba).
*
*/
int main()
{
// Let the user enter a expression
symbol x("x"), y("y");
string s;
cout << "Enter an expression containing 'x' and/or 'y': ";
cin >> s;
// Expression now in expr
ex expr(s, lst{x,y});
cout << "start integration of " << expr << " ..." << endl;
// Some definitions for VEGAS
#define NDIM 2
#define NCOMP 1
#define EPSREL 1e-3
#define EPSABS 1e-12
#define VERBOSE 0
#define MINEVAL 0
#define MAXEVAL 50000
#define NSTART 1000
#define NINCREASE 500
// Some variables for VEGAS
int comp, nregions, neval, fail;
double integral[NCOMP], error[NCOMP], prob[NCOMP];
// Our function pointer that points to the compiled ex
FUNCP_CUBA fp;
// Optionally, compile with custom compiler flags:
// setenv("CXXFLAGS", "-O3 -fomit-frame-pointer -ffast-math", 1);
compile_ex(lst{expr}, lst{x,y}, fp);
// Starting VEGAS
// By invocation of compile() the expression in expr is converted into the
// appropriate function pointer
Vegas(NDIM, NCOMP, fp,
EPSREL, EPSABS, VERBOSE, MINEVAL, MAXEVAL, NSTART, NINCREASE,
&neval, &fail, integral, error, prob);
// Show the result
cout << "result: " << integral[0] << endl;
return 0;
}
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