現代数学の系譜工学物理雑談古典ガロア理論も読む46

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398: 現代数学の系譜 雑談 古典ガロア理論も読む ◆e.a0E5TtKE  [sage] 2017/11/19(日) 20:45:33.01 ID:W1ZiI7BV

>>397 つづき
＜引用＞
http://www.unirioja.es/cu/jvarona/downloads/Differentiability-DA-Roth.pdf
DIFFERENTIABILITY OF A PATHOLOGICAL FUNCTION,
DIOPHANTINE APPROXIMATION,
AND A REFORMULATION
OF THE THUE-SIEGEL-ROTH THEOREM
JUAN LUIS VARONA
This paper has been published in Gazette of the Australian Mathematical Society, Vol-
ume 36, Number 5, November 2009, pp. 353{361.
Received 29 February 2008; accepted for publication 6 October 2009.
(抜粋)

ここに
fν(x)
＝0　if x ∈ R - Q（無理数）
＝1/q^ν  if x = p/q ∈ Q, irreducible （有理数で既約分数）
で

Theorem 1. For ν > 2, the function fν is discontinuous (and consequently not differentiable) at the rationals, and continuous at the irrationals.
With respect the differentiability, we have:
(a) For every irrational number x with bounded elements in its continued fraction expansion, fν is differentiable at x.
(b) There exist infinitely many irrational numbers x such that fν is not differentiable at x.
Moreover, the sets of numbers that fulfill (a) and (b) are both of them un-countable.
(引用終り)

http://rio2016.5ch.net/test/read.cgi/math/1510442940/398

481: 現代数学の系譜 雑談 古典ガロア理論も読む ◆e.a0E5TtKE  [sage] 2017/11/22(水) 19:18:43.01 ID:mEHYOxL2

>>480 つづき

Nevertheless, we choose this presentation because we find it the most interesting, as well as pedagogically useful.
For instance, “predicting the present” is a very natural way to think of the problem of guessing the value of f (t) based on f |(?∞, t).

2. THE μ-STRATEGY.
(詳細は略すので、原文ご参照。ここに引用するには、数学記号が複雑過ぎるので。)

P92
3. PREDICTING THE PRESENT.
(詳細は略すので、原文ご参照。ここに引用するには、数学記号が複雑過ぎるので。)

Corollary 3.4. If T = R and ∇ is <, then W0 is countable, has measure 0, and is nowhere dense.

What Corollary 3.4 tells us is that, if we model the universe as a function from the real numbers into some set of states, then the μ-strategy will correctly predict the present from the past on a set of full measure.
(In the following section, we show that, on a set of full measure, it correctly predicts some of the future as well.)
Note that these results concerning T = R are also valid when T is any interval of reals.
One needs to be cautious about interpreting this as meaning that the μ-strategy is correct with probability 1.
For a fixed true scenario, if one randomly selects an instant t in the interval [0,1] (or in R, under a suitable probability distribution), then
Corollary 3.4 does tell us that the μ-strategy will be correct at t with probability 1.
However, if one fixes the instant t, and randomly selects a true scenario, then the probability that the μ-strategy is correct at t under that scenario might be 0 or might not even exist, depending on how one defines the notion of a random scenario.

P95
W = {t ∈ R | the μ-strategy does not guess well at t }.
Theorem 5.1. The set W is countable, has measure 0, and is nowhere dense.

つづく

http://rio2016.5ch.net/test/read.cgi/math/1510442940/481

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