You get the error because, you have used incorrect syntax for squaring trignometric terms for defining delta_u.
The correct syntax is
cos(input).^2
%or if you want to use an extra set of parenthesis
(cos(input)).^2
You have not defined the variable x in your code above, thus we can not run your code and check for other errors.
However, off a quick glance, I spotted a few errors -
> You need to define the variables - x1, y1, x2, and y2 before using them.
> This code snippet is not valid for 2 reasons
P(0)=[0 0 0;0 0 0;0 0 0];
1st - Indexing in MATLAB starts with 1.
2nd - You can not allot more elements than the number of indices for numeric arrays. Assigning numeric values follows one-to-one correspondance.
Based on the use of this line of code, just use -
P = zeros(3);
%or
P0 = zeros(3);
You can name the variable anything which is accepted by MATLAB - https://in.mathworks.com/help/matlab/matlab_prog/variable-names.html
