There are several things wrong with this code.
First
while E~=0,2
is not valid Matlab syntax. Replace the , with a . if you mean to test for 0.2 (i.e., 1/5).
Second, you are resetting Io at the beginning of each loop so you will get the same results on every pass through the loop. Move the line
Io=45.4746;
above the while loop.
Third, this algorithm (if you move the initialization of Io outside the loop), converges to 1.0 and will never reach 0.2. So, you have an infinite loop.
