exampleMultiRoot.C File Reference

Example of using multiroot finder based on GSL algorithm. More...

Go to the source code of this file.

Detailed Description

Example of using multiroot finder based on GSL algorithm.

Find the root of Rosenbrock system of equations:

\[ f1(x,y) = a(1-x) \]

\[ f2(x,y) = b(y-x^2) \]

with:

\[ a = 1, b=10 \]

The MultiRootFinder is based on GSL and it requires the MathMore library installed

Usage:

>.x exampleMultiRoot.C()

or

>.x exampleMultiRoot(algoname,printlevel)

where algoname is for an algorithm not using the derivatives: hybridS (default) , hybrid, dnewton, broyden

Processing /mnt/vdb/lsf/workspace/root-makedoc/rootspi/rdoc/src/master/tutorials/math/exampleMultiRoot.C...
GSLMultiRootFinder::Solve:hybrids max iterations 100 and  tolerance 1e-06
GSL Algorithm used is :  hybrids
Number of iterations  =  19
Root values     = x[0] =            1   x[1] =            1   
Function values = f[0] =            0   f[1] = -6.17162e-11   

#include "RConfigure.h"

#ifdef R__HAS_MATHMORE
#include "Math/MultiRootFinder.h"
#endif
#include "Math/WrappedMultiTF1.h"
#include "TF2.h"
#include "TError.h"

// example of using multi root finder based on GSL
// need to use an algorithm not requiring the derivative
//like hybrids (default), hybrid, dnewton, broyden

using namespace ROOT::Math;
void exampleMultiRoot(const char * algo = 0, int printlevel = 1) {

#ifndef R__HAS_MATHMORE
   Error("exampleMultiRoot","libMathMore is not available - cannot run this tutorial");
#else

   ROOT::Math::MultiRootFinder r(algo);
    //defining the function
   // use Rosenbrock functions
   TF2 * f1 = new TF2("f1","[0]*(1-x)+[1]*y");
   TF2 * f2 = new TF2("f2","[0]*(y-x*x)");
   f1->SetParameters(1,0);
   f2->SetParameter(0,10);
   // wrap the functions
   ROOT::Math::WrappedMultiTF1 g1(*f1,2);
   ROOT::Math::WrappedMultiTF1 g2(*f2,2);
   r.AddFunction(g1);
   r.AddFunction(g2);
   r.SetPrintLevel(printlevel);

   // starting point
   double x0[2]={-1,-1};
   r.Solve(x0);
#endif
}

Author

Lorenzo Moneta

Definition in file exampleMultiRoot.C.