MATLAB: For loop – Error Attempted to access y(30); index out of bounds because numel(y)=2.

difference equationerrorfor loopinex out of boundstime path

Dear all
I have to compute a time path over t=1:100 periods. I have to assume a temporary shock in t=30:32 so I tried this and used different for loops:
y(1)=100; %(starting value of y) a=1.02;
    for t=1:29;
        y(t+1)=y(t)*(a+0.0001*randn(1,1));
        for t=30:32         (here there is the temporary shock)
            y(t+1)=y(t)*(a-0.2);
        end;
        for t=33:100
            y(t+1)=y(t)*(a+0.0001*randn(1,1));
        end;
    end;
Unfortunately, it gives me the error: Attempted to access y(30); index out of bounds because numel(y)=2.
I really tried different things but couldn't get the loop fixed.
I already thank you for answering my question.

Best Answer

Hi,
the best is to define y before you use it.
y=zeros(100,1)
I think your loops are nested in the wrong way. You set t = 1, calculate y(2), enter the next loop and calculate y(31), y(32) and y(33) and then enter the last loop to calculate the entries up to y(100). You do all of this for t = 2 to t = 29. I suggest you execute one loop after the other, this should save a lot of time.
Related Question