Passing external function of multiple variables as a function of one variable in Fortran

Question

I'm trying to use routines in QUADPACK to perform numerical integration. The routines expect functions to be passed as REAL,EXTERNAL, so I don't have the liberty of using pointers or whatever else.

Is it possible to alias a function f(x,a,b,...) as being a function f(x) for the routine that expects a function of x only? Much like what one would accomplish in MATLAB with @(x)f(x,a,b,...).

Answer 1

You cannot make similar tricks with functions in Fortran directly. You also cannot return a closure in Fortran. Just write a wrapper.

function wrap_f(x) result(res)
  ...
  res = f(a,b,...)
end function

It can be an internal or module function and get a and b by the host association or it can use the module containing a and b.

If you want to pass the function as an actual argument, it cannot be an internal procedure in up to Fortran 2003, but only in Fortran 2008. But it works in recent versions of gfortran and ifort. For better portability use a module.