[row,c]=size(x); % get dimensions of x
s=1; % s takes the value 1
for i=5:9:last_index % Array index values takes from 5 to last_index with difference of 9
var1=(s-1)*9+1; % creates a variables with this value
var2=s*9; % this value is 9
sd = std(x(var1:var2)); % calculates the standard deviation of values of x from var1 to 9.