MATLAB: Avoid negative index in array or matrix

negative index arrayoptimizationoptimization loopremove if/else

I'm working on 2 loops in which i have the difference of two indices like this:
for i=1:interval_1
  for j=0:interval_2
    if(i-j>0)
      X(i+1)=c(j+1)*X(i-j);
    else
      %nothing
    end
  end
In my situation interval_1 and interval_2 are more or less 1 million so i want to optimize and remove if/else. It would be useful if there exist a command which ignores operations with negative index. Tell me.

Best Answer

Just do this:
   for i=1:interval_1
     j = min(i-1,i2);
     X(i+1)=c(j+1)*X(i-j);
   end
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