Why is the Ruby Math.log function returning the wrong values?

Question

Given 3^5 (3**5 or 3*3*3*3*3) = 243.

Why/how does Ruby do the following:

n = 243
Math.log(n,3)
returns: 
4.999999999999999

Math.log(243)/Math.log(3)
returns: 
4.999999999999999

3**Math.log(n,3)
returns:
242.99999999999977

That last one really gets me. Something is going wrong here? I'm missing something? Both?

Thanks!

If you need arbitrary-precision floating point numbers, you can use the `flt` gem: `require 'flt/sugar'; D.math{log(3**5,3)}` But remember that it will degrade performance. — kxmh42, Sep 01 '16 at 17:58

score 1 · Answer 1 · answered Sep 01 '16 at 17:38

1

Values are not wrong, this is because floating point precision is limited.

answered Sep 01 '16 at 17:38

Vasfed

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Why is the Ruby Math.log function returning the wrong values?

1 Answers1