this is the code to find arithmetic mean and geometric mean in matlab code

x=[1,2,3;4,5,6;8,7,9]; y=sort(x(:)); z=numel(y); a=sum(y)/numel(y) b=(prod(y))^(1/numel(y))

the arithmetic mean is 5, the geometric mean is 4.1472 and the number of elements is 9.

i need to make a matlab code to find the variance without using the built in function.