Help me in debugging this code. Error : Unable to perform assignment because the left and right sides have a different number of elements.

clc; 
clear all; 
close all;

global th

% Define joint angles
th = struct( ...
    'th1', [0; 0; 0], ...
    'th2', [0; pi/4; 0], ...
    'th3', [0; pi/4; 0] ...
);

i = 1;

while (1)
    human(th);
    pause(0.1);
    i = i + 1;
    move1();
    cla;
end

th1_1: 0
th2_2: 0.7854

Unable to perform assignment because the left and right sides have a different number of elements.

Error in solution>move1 (line 39)
th.th2(2) = pi/4 + (pi/2) * index1;

%% Motion function
function move1()
    global th i
    k = [1:1:10 9:-1:2];  
    N1 = length(k);
    if i > N1
        i = i - N1;
    elseif i < 1
        i = i + N1;
    end
    
    % Interpolation index
    index1 = (k(i) - 1) / 9;
    
    % ERROR MAY OCCUR HERE
    th.th2(2) = pi/4 + (pi/2) * index1;  
    th.th3(2) = pi/4 - (pi/2) * index1;  
end

%% Human visualization function
function human(th)
    % Accessing angles
    th1_1 = th.th1(1);
    th2_2 = th.th2(2);
    
    % ERROR MAY OCCUR IF STRUCTURE INDEXING IS WRONG
    disp(['th1_1: ', num2str(th1_1)]);
    disp(['th2_2: ', num2str(th2_2)]);
end

So i am trying to make a humanoid moving. So for that i am modifying the theta(th) and i am getting this error but both the LHS and RHS is scalar. Still it is showing this error. Any ideas will help....

Answer 1

[Cris LaPierre]

You need to also declare i as global in your script.

[Walter Roberson]

That is to say, in your script you just assign to i without having declared it global.

Declaring something as global only affects the environments in which it is declared as global, not all environments with the same variable name.

If it were otherwise, then you would be able to affect security or banking functions by declaring global variables with the same name as the local variables within the function, which is obviously undesireable.