Non-static functions as arguments

[Audiority]

Hey guys,
I'm currently using a Newton-Raphson function that takes a function as a parameter

Code: Select all

typedef double (*func)(double)

inline double NewthonRaphson( func f, double x0)
{
   //do NR stuff
   ...
   return NewtonRaphson(f, x0);
}

The problem is that it only accepts static member functions and, those, won't accept global variables unless they are static too.

Is there a way to make that working without using static functions?

Thanks,
Luca

[Xenakios]

If you can use C++11 or newer, a solution is to use a function template and lambdas :

Code: Select all

template<typename F>
inline double NewthonRaphson( F f, double x0)
{
   //do NR stuff
   ...
   return NewtonRaphson(f, x0);
}

// To use, inside a class method :
double result = NewtonRaphson([this](double x){ return amemberfunctionofthis(x); },whateverparametergoeshere);

[Music Engineer]

nowadays (since C++11), i would use std::function for this (passed by const reference to your root finder). it can wrap functors (i.e. classes that implement the ()-operator for function evaluation) or lambda-functions (where you can, inside the lamda definition, call any member function of your object) or plain old function pointers. btw. wouldn't you have to pass a second function for evaluating the derivative? or are you planning to use numeric (finite difference) approximations? in this case, you are probably better off with regula falsi or even better brent's method

[Xenakios]

i would use std::function

It is probably slower than the template based solution I gave above. (It would depend on if the compiler can see through the std::function mechanisms and optimize them away.)

[vortico]

Here's a good implementation of what you're looking for. It uses the function template method described by Xenakios. https://github.com/VCVRack/Rack/blob/v0 ... sp/ode.hpp

[stratum]

For what it's worth, here is another toy https://github.com/cheind/cppopt

[Audiority]

Thanks guys. The lambda solution works like a charm.