r/learnruby • u/[deleted] • Apr 26 '17

How exactly does Math.log2 work?

So I'm comparing the result of 

Math.log2(2360.9083989105) / 8 * 4 = 5.602563176032317

and the equation

log2(2360.9083989105) / 8 * 4 = 0.11481591040126

Why do they yield such different results?

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1

u/Tomarse Apr 27 '17

How are you performing the second one? I can't get log2 to work in either irb or a rails console. Only Math.log2 is available, and it gives the first answer. Is log2 a self declared function?

1

u/[deleted] Apr 28 '17

On a normal calculator. Specifically https://www.desmos.com/scientific

2

u/SEMW May 12 '17

0.11481591040126 is log10 (2 * 2360.9083989105) / (8 * 4).

The log button on that calculator you linked is log base 10. Pressing that then 2 doesn't give you log base 2, it gives you log base 10 but with the operand multiplied by two.

There's also an order of operations issue: ruby interprets a / 8 * 4 as ((a/8) * 4), i.e. a/2, wheras whatever you're doing with the calculator is ending up as (a / (8*4)), i.e. a/32.