Quality of rational approximations

  • Context: Undergrad 
  • Thread starter Thread starter Vanadium 50
  • Start date Start date
  • Tags Tags
    Quality Rational
Click For Summary

Discussion Overview

The discussion centers on the quality of rational approximations for various mathematical constants, particularly π, e, and √2. Participants explore the effectiveness of small integer ratios in approximating these constants and consider potential underlying reasons for the differences in approximation quality.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • One participant claims that 22/7 is a good approximation for π, while noting that √2 and e require larger ratios for similar accuracy, specifically mentioning 99/70 for √2 and 193/71 for e.
  • Another participant suggests that the pattern of continued fractions might explain the differences in approximation quality.
  • A subsequent reply questions what is special about π, noting that e also has a continued fraction representation.
  • One participant argues that algebraic numbers are not well approximated by rationals if the denominators are kept small, referencing Roth's theorem as a basis for this claim.
  • A mention of Dyson's work in this area adds historical context to the discussion.

Areas of Agreement / Disagreement

Participants express differing views on the reasons behind the varying effectiveness of rational approximations for different constants, indicating that multiple competing perspectives remain without a clear consensus.

Contextual Notes

The discussion does not resolve the assumptions regarding the nature of the constants or the implications of Roth's theorem on approximation quality.

Vanadium 50
Staff Emeritus
Science Advisor
Education Advisor
Gold Member
Dearly Missed
Messages
35,005
Reaction score
21,705
22/7 is a very good approximation for π. Sqrt(2) doesn’t do that well until 99/70 and e doesn’t do that well until 193/71. 355/113 is even better.

Is there some reason for this? Perhaps geometrical? Why do the ratios of small integers work better for π than other numbers? Or is it just coincidence? ("Gotta be something...")
 
Mathematics news on Phys.org
The pattern of continued fractions?
 
Sure, but e has one too. What's special, if anythnig, about pi?
 
If you want to keep the denominators of the rationals somewhat small, then algebraic numbers are not well approximated by rationals.
https://en.wikipedia.org/wiki/Roth's_theorem

ps. Interesting that Dyson had worked on these matters.
 
  • Like
Likes   Reactions: Vanadium 50, FactChecker, PeroK and 1 other person

Similar threads

  • · Replies 7 ·
Replies
7
Views
2K
Replies
7
Views
4K
  • · Replies 4 ·
Replies
4
Views
4K
  • · Replies 7 ·
Replies
7
Views
4K
  • · Replies 4 ·
Replies
4
Views
3K
  • · Replies 72 ·
3
Replies
72
Views
10K
  • · Replies 1 ·
Replies
1
Views
3K
  • · Replies 21 ·
Replies
21
Views
4K
Replies
2
Views
818
  • · Replies 2 ·
Replies
2
Views
2K