how to modify the following code using quad

function f=fun(x)
x=(-4:0.1:4);
y=x.^3-2*x.^2-5*x+6;
q=quad(fun,-4,4);  

plot(x,q,'--r'); 

end

I was trying to compute and plot the integral for y=x.^3-2*x.^2-5*x+6 ;x>=-4 and x<=4. I used quad function in order to do that. I get the following error:

Undefined function or variable 'fun'.

Error in integralatema (line 4)
q=quad(fun,-4,4);

Can someone please tell me how can i modify the code in order to run it error-free? Thank you.

Answer 1

[Star Strider]

If you want to call a function file you have to create a function handle for it with the ‘@’ operator. In the situation you illustrated, you would call it as

q = quad(@fun,a,b);

That said, do not call your function from inside your function! It would have created recursion problems even if it would have worked. (It wouldn’t have, because quad wants two limits for its integration, not a vector.)

So simply use quad with an anonymous function expression for your function, and your limits:

y= @(x) x.^3-2*x.^2-5*x+6;          % Anonymous Function
q=quad(y, -4, 4);                   % Integrate

producing a value for ‘q’ of about -37.3.