problem with sum in function

Hello every one!

I am new with matlab and i have a problem with very simple program with matlab 2019a

Code 1:

clear all;
z=so;
function [s] = so
    A=[1 5 3 4 2 10 21 65];
    s = sum(A);
    s = s+1;
end

The answer is z=112, it's correct

Code 2:

clear all;
A=[1 5 3 4 2 10 21 65];
z=so;
function [s] = so
    s = sum(A);
    s = s+1;
end

I get this error

So as far as i understand, "Sum" can not read the variable out of the function "so".

DId i do somethings wrong or my computer have issues?

It's just a little test, but i need to get work with "sum" in a function so I can write a bigger program.

Answer 1

[Steven Lord]

That is correct. Functions operate in their own workspaces.

Variables from outside the function generally only enter a function's workspace when passed as input arguments to the function.

Variables from inside the function generally only leave the function's workspace to enter a different workspace when returned from the function as an output argument.

Functions generally can't access variables outside their own workspace.

[Those rules aren't technically complete, but when you're starting out they're a good mental model to use as a starting point for your MATLAB knowledge.]

In your first example you created the variable A inside so's workspace so the so function has access to the A variable. Since you didn't return A from so, A is not added to the workspace from which so was called when the so function returns.

In your second example you created A outside so's workspace and didn't pass it in as an input, so the so function doesn't have access to the A variable.

[ronaldo messi]

i understand now, thank you Steven!

Answer 2

[Fangjun Jiang]

You are right. All you need to do is "function [s] = so(A)" to pass in the value of A.

[ronaldo messi]

how fool i am. Thank you so much Fangjun Jiang!

[Steven Lord]

You're not a fool. You said you're new with MATLAB, and that means there are things you don't know. That's how everyone, with the possible exception of Cleve, started out. And Cleve is a bit of a special case, being the author of the first version of MATLAB.