Consider the following example. a and b are two random variables. The loop will exit if and only if a+b=1. Is it true or false?
a=rand; b=rand; while(a+b == 1) a=rand; b=rand; end
While executes as long as the given condition is true, so the loop would only execute as long as the sum was 1.
Note: please take time to review the following: http://matlab.wikia.com/wiki/FAQ#Why_is_0.3_-_0.2_-_0.1_.28or_similar.29_not_equal_to_zero.3F