Functions
std::pair< G4double, G4double >	bracketRoot (RootFunctor const *const f, G4double x0)
	Bracket the root of the function f. More...

Variables
const G4int	maxIterations =50
	Maximum number of iterations for convergence. More...

const G4double	toleranceY = 1.e-4
	Tolerance on the y value. More...

Function Documentation

◆ bracketRoot()

std::pair< G4double, G4double > G4INCL::RootFinder::anonymous_namespace{G4INCLRootFinder.cc}::bracketRoot	(	RootFunctor const *const	f,
		G4double	x0
	)

Bracket the root of the function f.

Tries to find a bracketing value for the function root.

Parameters

f	pointer to a RootFunctor
x0	starting value

Returns: if the root could be bracketed, returns two values of x bracketing the root, as a pair. If the bracketing failed, returns a pair with first > second.

Definition at line 75 of file G4INCLRootFinder.cc.

                                                                                       {
        G4double y0 = (*f)(x0);
 
        const G4double scaleFactor = 1.5;
 
        G4double x1;
        if(x0!=0.)
          x1=scaleFactor*x0;
        else
          x1=1.;
        G4double y1 = (*f)(x1);
 
        if(Math::sign(y0)!=Math::sign(y1))
          return std::make_pair(x0,x1);
 
        const G4double scaleFactorMinus1 = 1./scaleFactor;
        G4double oldx0, oldx1, oldy1;
        G4int iterations=0;
        do {
          if(iterations > maxIterations) {
            INCL_DEBUG("Could not bracket the root." << '\n');
            return std::make_pair((G4double) 1.,(G4double) -1.);
          }
 
          oldx0=x0;
          oldx1=x1;
          oldy1=y1;
 
          x0 *= scaleFactorMinus1;
          x1 *= scaleFactor;
          y0 = (*f)(x0);
          y1 = (*f)(x1);
          iterations++;
        } while(Math::sign(y0)==Math::sign(y1)); /* Loop checking, 10.07.2015, D.Mancusi */
 
        if(Math::sign(y1)==Math::sign(oldy1))
          return std::make_pair(x0,oldx0);
        else
          return std::make_pair(oldx1,x1);
      }