Calling a function within another function

So I'm writing a bisection method. The beginning of the method looks like this.

function root = Bisect ( xl , xu , eps , imax, f )
i = 1;
fl = f(xl);

So I pass in xl (note that l is the letter L and not a one) when I call this function and it then calls the function f. Here's my function f:

function y = f(x)

      y = (pi*x^2)*((3*4.1 - x)/3);

end

The problem is that I called the bisection function with the input "Bisect(0, 4.1, 0.0001, 20, f)" and I keep getting this error:

>> Bisect(0, 4.1, 0.0001, 20, f)
  Not enough input arguments.

    Error in f (line 3)
    y = (pi*x^2)*((3*4.1 - x)/3);

So what am I doing wrong?

Answer 1

[Steven Lord]

That tries to call the function f with 0 inputs and pass the value returned by that call into the Bisect function as the fifth input. You instead want to pass a function handle to f into the Bisect function as the fifth input, so that later on Bisect can call f using that function handle.

Bisect(0, 4.1, 0.0001, 20, @f)

You'd see the same behavior if you did something like:

fzero(sin, 1) % will error because sin needs 1 input

instead of:

fzero(@sin, 1)

or:

fzero(@(x) sin(x), 1)

[Brandon Macleod]

Thanks.

Answer 2

[Matt J]

Use '@' to specify a handle to f(),

 Bisect(0, 4.1, 0.0001, 20, @f)