input argument "x" is undefined

[daher]

Hi All

I am new with Matlab

I am trying to write a function on an M-file; here is the script:

function f = ali(x)
f = - x(1) * x(2);
A = [-1 -2 -2; 1 2 2]
b = [0; 72]
x0 = [10; 10; 10];
[x,fval] = fmincon(@ali,x0,A,b)

Whenever i run it i get the following message;
input argument "x" is undefined

So can anybody help

Best Regards