MATLAB: What does this code do

for loopsloops

I am picking up on someone else's code and I am having trouble understanding the meaning of the following lines: 
[row,c]=size(x);
s=1;
for i=5:9:last_index  %runs for total number of samples in signal      
    var1=(s-1)*9+1;
    var2=s*9;
    sd = std(x(var1:var2));

Best Answer

[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.
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