You do not ask to output a matrix. You output a string to the display, and you ask to plot() something. You do not appear to have hold on in effect, so each plot() will overwrite the previous plot.
Also, your loop does not use n . It does, however, use i . It is not obvious from your code whether you assigned something to i. If you did not, then i will have its default value of sqrt(-1) . If you intend it to be sqrt(-1) then it would be clearer if you code 1i instead of i .
I recommend that you read