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All Rational Approximations of Pi Are Useless

blog.wolfram.com

11–20 of 113 posts

Re: All Rational Approximations of Pi Are Useless

#11
post #6

Ok, I'm confused, what exactly is the point here? If you don't care, 3.14 is sufficient, if you do care then you use π, and if you really care you use τ[1]. [1]( http://tauday.com/tau-manifesto ) (And if you really really really care, you use a different font then the one HN defaults too.)

The point is that you should just memorize whatever precision decimal you need. There's no shortcut like 22/7 that will magically give you more accuracy and be easy to memorize.

Re: All Rational Approximations of Pi Are Useless

#12
post #2

I think the reason for this is Thue–Siegel–Roth theorem that says there are only finitely many "good" rational approximations of pi (or any other irrational number).

The Thue–Siegel–Roth theorem deals specifically with algebraic numbers, of which pi is not one.

Re: All Rational Approximations of Pi Are Useless

#13
post #6

Ok, I'm confused, what exactly is the point here? If you don't care, 3.14 is sufficient, if you do care then you use π, and if you really care you use τ[1]. [1]( http://tauday.com/tau-manifesto ) (And if you really really really care, you use a different font then the one HN defaults too.)

Did you read the article? He explains very precisely what he means and what his conclusion is. "Rational" in the context of the title means "one integer divided by another to which the first is relatively prime", and the word "useless" indicates that there is no gain in accuracy/complexity in comparison to the decimal notation for a rational number (where you express a rational number as an integer divided by an implicit power of ten).

Re: All Rational Approximations of Pi Are Useless

#14
post #4

3.1415927 is really just a shorthand for 31415927/10000000, so shouldn't it count as 17 characters rather than 9?

No it isn't. It isn't "a shorthand". It is a notation. Of those two notations, no one is "a shorthand" of another.

I think the point is that McLoone is using two different notations and measuring an artifact of this. There's nothing special about base-10 denominators.

Re: All Rational Approximations of Pi Are Useless

#16
Very neat: naive attempts to memorize Pi with rational-number shortcuts (i.e., fractions with integers in the nominator and denominator, such as 22/7 and 355/113) seem pointless, because getting more decimal digits of Pi right requires that one memorize a correspondingly larger number of digits in the numerator and/or denominator, defeating the purpose of these native attempts.

--

PS. The author is offering a prize to the reader who finds the rational number which gets the most decimals of Pi right for every digit of such rational number that has to be memorized. (Note that only rational numbers are allowed -- that is, fractions with integers in the numerator and denominator. Using formulas or numbers that are not rational is not allowed in the competition.)

Re: All Rational Approximations of Pi Are Useless

#18
post #16

Very neat: naive attempts to memorize Pi with rational-number shortcuts (i.e., fractions with integers in the nominator and denominator, such as 22/7 and 355/113) seem pointless, because getting more decimal digits of Pi right requires that one memorize a correspondingly larger number of digits in the numerator and/or denominator, defeating the purpose of these native attempts. -- PS. The author is offering a prize t…

I might be different, but 355/113 is very easy to remember and is not 7 unique segments of information. I just think "double the odds"

113355

We know we want a fraction, not a single number, so split down the middle:

113/355

And we know pi won't be less than 1, so flip it: 355/113. Knowing that the digits sequences are doubled lets you do some cheap, mental run length encoding. In a case where you need a hand calculation, spending 3 seconds to re-derive the sequence seems tolerable.

Re: All Rational Approximations of Pi Are Useless

#19
post #14

Earlier quoted context omitted.

No it isn't. It isn't "a shorthand". It is a notation. Of those two notations, no one is "a shorthand" of another.

I think the point is that McLoone is using two different notations and measuring an artifact of this. There's nothing special about base-10 denominators.

He's comparing apples to apples. Kolmogorov complexity for different ways to approximate п is more or less flat at bang for the buck.

Re: All Rational Approximations of Pi Are Useless

#20
post #4

3.1415927 is really just a shorthand for 31415927/10000000, so shouldn't it count as 17 characters rather than 9?

No it isn't. It isn't "a shorthand". It is a notation. Of those two notations, no one is "a shorthand" of another.

Still, it is a rational approximation of pi.
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