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# "Local function"?

Hi all,

Suppose I have a routine to find the maximum
of any *univariate* function f in the interval [a, b]:

double f(double x);
double findmax(double (*func)(double), double a, double b);

Now I have a function with three variables:

double g(double x, double y, double z);

And I want to find the maximum of g, with y=y0 and z=z0 fixed, and
x in the interval [a, b].

How can I achieve this? Since C++ does not allow local functions,
the only thing I can think of right now is to modify the findmax
function:

double findmax(double (*func)(double, double, double),
double y, double z, double a, double b);

However, this means if someday I have another function h with four variables,
I'll have to modify findmax again. How can I have a universal findmax?

jack
Jul 19 '05 #1
1 3904
"jack" <id***@yahoo.com> wrote...
Suppose I have a routine to find the maximum
of any *univariate* function f in the interval [a, b]:

double f(double x);
double findmax(double (*func)(double), double a, double b);

Now I have a function with three variables:

double g(double x, double y, double z);

And I want to find the maximum of g, with y=y0 and z=z0 fixed, and
x in the interval [a, b].

How can I achieve this? Since C++ does not allow local functions,
It doesn't allow stand-alone local functions, but you can have
a local type with an inline member function, which will act just
like a local function.
the only thing I can think of right now is to modify the findmax
function:

double findmax(double (*func)(double, double, double),
double y, double z, double a, double b);

However, this means if someday I have another function h with four variables, I'll have to modify findmax again. How can I have a universal findmax?

You need to define your 'findmax' not in terms of a function pointer
but in terms of a functor. Try this

template<class T, class F>
T findmax(F func, T a, T b)
{
.. // do what you do, but replace 'double' with T if needed
}

That will allow you to use 'bind2nd' and 'bind1st' function adapters
with which you could "fix" some arguments and let others do the job.

C++ book.

Victor
Jul 19 '05 #2

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