Trapezium Rule example won't work?

I do not understand why this code is not working? I am trying to estimate the integral of e^-x2 between x=0 and x=2 using the trapezium rule

Answer 1

[Steven Lord]

You're combining a function declaration and a function call.

Call your function something other than trapz because that's already a function in MATLAB. Let's call it IssieTrapz. It takes four input arguments, which I suspect your function accepts in the following order:

function I = IssieTrapz(f, a, b, n)

This is line 1 of your function. It replaces your original line 1. That's the declaration of the IssieTrapz function.

Now when you call IssieTrapz, that's when you specify the function and give values for a, b, and n.

result = IssieTrapz(@(x) exp(-x^2), 0, 2, 10);

[Issie]

Okay, I have replaced line 1 with what you suggested.

But I am still unsure as to what you mean by the second bit and where I would put this in my code? Do you not have to define what f is?

[Steven Lord]

That second line doesn't go inside your function. That's how you call (use) your function. Type it in the Command Window. When you call your function like that, whatever you pass in as the first input argument will be assigned the name f inside your function. So for this call, f is @(x) exp(-x^2).

You could call it a second time with a different function to change what f is. If you called it like this:

result2 = IssieTrapz(@cos, -pi, 2*pi, 42)

f would be @cos for that call to IssieTrapz.

See this documentation page for a brief introduction to calling functions.