Matlab I am trying to write a function on an M-file

[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

 

[Pythagorean]

you have to define x when you call the function. How are you running the function?

I would suggest using the command window and calling it with:

f = ali(x)

where x is whatever two numbers you want it to be.

in your second line, you call x(1) and x(2) so there has to be two elements in x
so at your command window, you could enter:

f = ali([5 7]) where I've chosen 5 and 7 arbitrarily.

 

[tacman]

,

First of all, welcome to Matlab! Writing functions in M-files can seem a bit daunting at first, but with some practice and guidance, you'll get the hang of it.

In your code, it looks like you are trying to use the variable "x" as an input argument for your function "ali". However, when you call the function using the fmincon function, you are also defining a variable "x" which is causing the error.

To fix this, you can change the input argument of your function to something else, like "input_x". So your function would look like this:

function f = ali(input_x)

Then, when you call the function using fmincon, you can use a different variable name, like "input_x0". So your fmincon call would look like this:

[x,fval] = fmincon(@ali,input_x0,A,b)

This should fix the error and allow your function to run properly. Keep practicing and don't hesitate to ask for help when needed. Good luck!