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Re: [Help-gsl] GSL, C++, and function pointers

From: Jordi Gutierrez Hermoso
Subject: Re: [Help-gsl] GSL, C++, and function pointers
Date: Tue, 6 Mar 2007 15:18:31 -0600

On 05/03/07, eknecronzontas <address@hidden> wrote:
[T]he easiest solution is to write a global (or static member)
function wrapper with the same form as GSL expects and then calling
your function instead.

I think this is what I'll do.

     My solution to this problem is usually to rewrite
the GSL routines as templates so they call
type::operator() instead of using a function pointer.


I should note the GSL derivative function is quite
simple and probably not to difficult to
case you decide you want to do that instead.

I would prefer to not do this, as I am hoping that my code will be
"portable" or as portable as the GSL itself. There are a number of
machines on which this will compile, and I don't have root access to
all of them. They already have the GSL installed on them, and I'd
rather not modify the GSL itself.

I would send patches instead ;-) but it seems that operator() is a
strictly C++ construct.

Thank you for your thoughts.

As for Sr. Jabardo's thoughts....

On 05/03/07, Paulo Jabardo <address@hidden> wrote:
If I understand you correctly, you need to write a
wrapper class.

Yes, I think this is what I'll do. But doesn't the STL already have
wrapper classes precisely for situations like this? I don't really
understand how to use the STL classes defined in <functional>, so I'm
not sure if they really solve my problem or not.

a function pointer to a function that accepts a double
and a void* and returns a double and a second field
that is a void*.

Void pointers scare me. They're too much like unprotected C. :-)

The params field is a pointer to user data. It can be
anything you want so you can define a structure/class
that contains every information necessary. Then you
write a global function (as defined by GSL) that knows
how to use this structure/class you defined.

I don't understand how this is supposed to work, so I'll avoid it. My
wrapper class will take care of the param fields by having them as
data members.

One final question for the floor. Why doesn't the GSL have
higher-order differentiation routines? Am I supposed to repeatedly
call the first order derivative in some way, or what? That seems a
little odd; almost "all" of the interesting differentiation occurs at
least with second derivatives. How am I supposed to procure those with
the GSL?

Thanks again,
- Jordi G. H.

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