Why am I receiving "Subscript indices must be real positive integers or logicals" error in my Euler's method code.

This is the code I am using to try to implement Euler's method and I keep receiving the above error at the 'f=' line. The function that is supposed to go there is this: y'(t) = t^-2(sin(2t)-2ty(t)). I have no experience with MatLab at all and have been fumbling my way through this whole course. Thanks for anybody who can help!

h = 0.25;  % step size
t = 1:h:2;  % the range of x
y = zeros(size(t));  % allocate the result y
y(1) = 2;  % the initial y value
n = numel(y);  % the number of y values
% The loop to solve the DE
for i=1:n-1
    f=t.^-2*(sin(2*t)-2*t*y(t));
    y(i+1)=y(i)+h*f;
end

Answer 1

[Rajanya]

Hi @cpv008,

The mentioned error is because of incorrect indexing of array 'y'. In MATLAB, all array indices must be logical or positive numeric integers.

Here in the code provided, 't' is a double array containing fractional(non-integral) numbers -

h = 0.25;  % step size
t = 1:h:2;  % the range of x
t

t = 1×5

1.0000 1.2500 1.5000 1.7500 2.0000

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As a result, 'y(t)' in the following line throws the error since y(<non-integral index>) is not allowed.

f=t.^-2*(sin(2*t)-2*t*y(t));

You can also refer to a similar question for more insight - https://www.mathworks.com/matlabcentral/answers/423701-subscript-indices-must-either-be-real-positive-integers-or-logicals.

Thanks.