Array indices must be positive or logical values

I am trying to conduct Implicit Midpoint and I am getting stuck. Why does this error appear? It is also coming up for my Adams-Bashforth.

clc

clear

close all

f= @(x,y)(-50*(y-cos(x)));

N = 100;

T = 1;

y0 = 0;

h = T/N;

x= (0:h:1);

y = zeros(N+1,1);

y(1) = y0;

for i = 1:N

j = i+0.5

y(i+1) = y(i) + h*f(x(j), y(j));

end

Answer 1

[Steven Lord]

for i = 1:N
   j = i+0.5
  y(i+1) = y(i) + h*f(x(j), y(j));
end

There's no such thing as the 1.5th element of either x or y in MATLAB, which is what you're trying to use as inputs to f on the third line of this code segment. Numeric indices must be real positive finite integer values.