There are several flaws and unclear issues in your script:
(1) What is your given system of ODEs with x,y,z variables?
(2) F_xyz, G_xyz, O_xyz need to be defined properly via anonymous function, function file, inline function or directly or matlabFunction. They are not defined properly within your script.
(3) within the loop [for .. end], x, y, z need to be calculated. In your script, x is missing and O_xyz is missing. From your statements, presumably you are trying to compute x, y, z. The defined x =0:h:1 is time space???
(4) ICs for x0, y0, z0 need to be defined correctly
(5) Memory allocation can be adjusted a bit more accurately, e.g. y = [y(1), zeros(1, numel(x)-1)]; ...