Array results showing negative values

[row,c]=size(x); 
total_frames=row/9;
k=1;
i=5;
aa=rem(row,P+1);
last_index=row-aa;
for i=5:9:last_index %runs for tatal number of samples in signal
   g =[x(i-1), x(i-2), x(i-3), x(i-4)];
   h =[x(i), x(i+1), x(i+2), x(i+3), x(i+4)];
   

So I am using this code x(i-1)...x(i-4) to go backward in the array but every time it subtracts and give results in negative. How will I go and select the backward values 1 to 4 before 5, because my loop start from 5.

   j = [g,h];
   theeta = std(j);
    alpha = 0.9;
    thresh = theeta * alpha;
end

[KSSV]

You can use fliplr and use same forward notation.