x = linspace(0,pi,100);
y = cos(x);
This probably isn't what you want. Perhaps you mean z = zeros(size(x)) or something similar.
z = size(x);
[row,col] = size(x);
for i = 1:col
z(i) = 1-x(i)^2/2 + x(i)^4/24;
end
Original code missing a divide by 2 on the second term in z1
%z1 = 1-x.^2+x.^4/24;
z1 = 1-x.^2/2+x.^4/24;
plot(x,z,x,z1);
Difference = z-z1 % To know the difference if the plot above isn't clear
