You cannot compare floating point numbers obtained through different methods with ==. This is true for all computer languages. This is due to the fact that many numbers cannot be represented exatly as floating point numbers (0.1 is one of them) and therefore small errors accumulate differently depending on the operations you perform.
For more details, see why is 0.3-0.2-0.1 not equal to zero. From your floor test you can see than optimal_distance is slightly smaller than 2 while temp_distance is either exactly 2 or slightly larger than 2. By slightly, we're talking of a difference most likely around or smaller than 1e-16.
The proper way to compare floating point number is to compare their difference to a small enough tolerance for your calculatios. In your case:
abs(optimal_distance - optimal_distance) < 1e-10
is probably appropriate.
