Your problem is caused by the fact that not all values of i will be exact integers, and that is due to the round-off errors in representing the value 0.1. The double precision floating point numbers matlab is using cannot achieve 0.1 exactly, so when you multiply their multiples by ten, the result is occasionally not an exact integer.
In your for-loop you should have written:
for i = 1:10000
t = i/10;
rather than
for t=0.1:0.1:1000
i=t*10;
to ensure integer values for i.
By the way, you should never call any of your variables 'pi'. That is a reserved word in matlab standing for the universal ratio between a circle's circumerence and its diameter. When you redefine it as you have, you may receive some unpleasant surprises along the way.
