RE: newbie: function of function of function ...

[Richardson, Anthony]

> From: address@hidden [mailto:help-octave-
> address@hidden On Behalf Of Dot Deb
> Sent: Thursday, September 27, 2012 2:26 PM
> To: address@hidden
> Subject: newbie: function of function of function ...
> 
> Maybe the subject can be misleading but expresses well my confusion.
> It is my n-th attempt with octave and every time I try I I get stuck with some
> "stupid" problem.
> This time I decided to go on and ask for help.
> 
> I think the problem is trivial but I just don't see the solution.
> 
> I need a funcioin that computes the integral (using something like quadgk or
> quadcc) from -Inf to +Inf of an integrand like this:
> 
> f(x) * log( f(x) )
> 
> where f is the argument of the function
> 
> Naively, should read as:
> 
> function retval = entropy( f )
>   quadcc( f*log(f), -Inf, +Inf)
> end
> 
> I know that, if I define a somewhere function, say "gauss", I can write
> 
> f = @(x) -gauss(x) .* log( gauss(x) );
> quadcc(f,-Inf,+Inf)
> 
> and it gives the right result.
> 
> The problem is that I need to include the two lines above in a function that
> uses another function name as argument.
> And I couldn't sort it out :(
> 
> Alberto

Try defining the entropy function like this:

function retval = entropy( f )
   quadcc( @(x) f(x).*log(f(x)), -Inf, +Inf)
end

and call it using:  entropy(@gauss)

Tony Richardson