Practice function function won't work for "humps"

I'm in the process of working through a book of practice problems, and I'm stuck on one that asks me to write a function function that returns the difference between a passed function's maximum and minimum values for a given range, and then plots the function for that range.

This is what I have so far:

function fdif = funcdif( f,X )
%Calculates the difference between an input function's maximum 
%and minimum values for a given range
%input: 
%   f = input function 
%   X = range of function (with increment) 
%output: 
%   fdif = difference between maximum and minimum values

fval = f(X);
fmax = max(fval)
fmin = min(fval) 
fdif = fmax - fmin;

plot(X,fval)
end

I've run it for

f = @(t)(10*e.^(-.25*t)).*sin(t-4) for t = 0:pi/32:6*pi

and for

v = @(x)(e.^(5*x)).*(sin(1./x)) for x = .01:.0001:.2

and it works fine for both. (Obviously, I'd assigned e = exp(1).)

However, when I try to use it for the built-in "humps" function with X = 0:.01:3, I get an error that says

"Subscript indices must either be real positive integers or logicals.

Error in funcdif (line 10) fval = f(X);"

However, when I run the steps of the function in the command window, it works fine. For the record, when I try to plug in the "humps" function, this is what I'm putting into the command line:

X = (0:.01:3)';
funcdif(humps,X)

Can anyone help me figure out what the problem is? Most appreciated.

[EDITED, Code formatted, Jan]

Answer 1

[Jan]

This provides the output of humps() as input to funcdif:

funcdif(humps,X)

But you want to provide a handle to the function:

funcdif(@humps,X)

[Jack Dempsey]

Thanks! That was what I needed to do!