How to check dependencies of floats

Question

I want to determine (in c++) if one float number is the multiplicative inverse of another float number. The problem is that i have to use a third variable to do it. For inst

Answer 1

You will have to precisely define what it means for two approximations to be multiplicative inverses. Otherwise, you won't know what it is you're supposed to be testing.

0.2 has no exact binary representation. If you store numbers that have no exact representation with limited precision, you won't get answers that are exactly correct.

The same things happens in decimal. For example, 1/3 has no exact decimal representation. You can store it as .333333. But then you have a problem. Are 3 and .333333 multiplicative inverses? If you multiply them, you get .999999. If you want the answer to be "yes" you'll have to create a test for multiplicative inverses that isn't as simple as multiplying and testing for equality to 1.

The same thing happens with binary.