Wednesday, 10 October 2007

mg.metric geometry - Sequences of evenly-distributed points in a product of intervals

One way to interpret this result is that it comes from the periodicity of the continued fraction expansion of phi=1+frac11+frac1cdots in the sense that it has no "better-than-expected" rational convergents, whereas for example with pi=(3;7,15,1,292,cdots) we may stop at the 292 to get a good approximation (355/113 I believe).



So one may look at numbers of the form xn=(n;n,n,n,cdots), which satisfy xn2nxn1=0, or xn=fracn+sqrtn2+42. So a few good sequences may be for example leftnx2right where x2=1+sqrt2, the so-called "silver ratio", or the same for x3=(3+sqrt13)/2.



EDIT: These are in some cases pretty good approximations; one way to measure the "well-distribution" of such a sequence is to take the fractional parts lfloornxnrfloor:n=1,cdots,M, sort them, compute the maximum difference between consecutive terms, and multiply this by M to get some number in the range [1,M). This can be accomplished in one line in Mathematica as follows:



WellDistribution[x_,M_]:=
Max[Differences[Sort[Table[N[FractionalPart[x*m]], {m, 1, M}]]]]*M;


Some interesting things happen with this when we vary n; perhaps I'll make a new post out of it.

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