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functor - a function wrapper suitable for field expressions

functor(2rheolef) rheolef-6.7 functor(2rheolef)

NAME

functor - a function wrapper suitable for field expressions

DESCRIPTION

A functor is a class-function, i.e. a class that defines the operator(): it can be used in place of an usual function. Moreover, functors can be used in Rheolef field expressions, mixed with fields (see field(2)). For instance, assuming that uh is a field and u_ex is a functor:
 
    Float err_l1 = integrate (omega, abs(uh - uh_ex), qopt);
 
where omega denotes a mesh (see geo(2)) and qopt a quadrature formula (see quadrature_option_type(2)). See also the integrate(4) function. An usual function u_ex_f cannot always be mixed so nicely in expressions, due to c++ language rules. For instance, the following exprtession is valid:
 
    Float err_l1 = integrate (omega, abs(uh - u_ex_f), qopt);
 
In some case, the compiler cannot build a field expression using usual functionsn e.g.
 
    Float I = integrate (omega, 0.5*u_ex_f), qopt);
 
because 0.5*u_ex_f is a direct algebraic operation between usual functions and flmoating points, that is not defined in the c++ language. A way to circumvent this difficulty is to convert the usual function into a functor, as in:
 
    Float I = integrate (omega, 0.5*functor(u_ex_f)), qopt);
 

IMPLEMENTATION

template<class R, class... Args>
std::function<R(Args...)>
functor (R(*f)(Args...)) {
  return std::function<R(Args...)>(f);
}
 
 

SEE ALSO

field(2), geo(2), quadrature_option_type(2), integrate(4)
rheolef-6.7 rheolef-6.7