[過去ﾛｸﾞ] 現代数学の系譜 工学物理雑談 古典ガロア理論も読む48 (625ﾚｽ)
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493(1): 現代数学の系譜 雑談 古典ガロア理論も読む ◆e.a0E5TtKE [sage] 2017/12/24(日) 10:30:23.82 ID:Q5UHveEY(6/18) AAS
>>492 つづき
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[4] Bohus Jurek, "Sur la derivabilite des fonctions a
variation bornee", Casopis Pro Pestovani Matematiky
a Fysiky 65 (1935), 8-27. [Zbl 13.00704; JFM 61.1115.01]
It appears that Jurek proves some general results
concerning the zero Hausdorff h-measure of
sets of non-differentiability for bounded
variation functions such that the sum of the
h-values of the countably many jump discontinuities
is finite (special case: h(t) = t^r for a fixed
0 < r < 1). General "h-versions" of the ruler
function seem to appear as examples, and V. Jarnik's
more precise results about the Hausdorff dimension
of Liouville-like Diophantine approximation results
are used.
This paper is on the internet at
http://dz-srv1.sub.uni-goettingen.de/cache/toc/D98714.html
http://dz-srv1.sub.uni-goettingen.de/sub/digbib/loader?ht=VIEW&did=D98723
つづく
494(2): 現代数学の系譜 雑談 古典ガロア理論も読む ◆e.a0E5TtKE [sage] 2017/12/24(日) 10:30:54.63 ID:Q5UHveEY(7/18) AAS
>>493 つづき
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[15] Gerald Arthur Heuer, "Functions continuous at the
irrationals and discontinuous at the rationals",
American Mathematical Monthly 72 #4 (April 1965), 370-373.
[MR 31 #3550; Zbl 131.29201]
Let f(x) = 0 if x is irrational, f(p/q) = |1/q| if
p and q are relatively prime integers, and f(0) = 1.
We say that a function g is Lipschitzian at x if there
exists a neighborhood U of x and a number M > 0 such
that |g(x) - g(y)| <= M*|x - y| for all y in U.
THEOREM 2: The function f^r is: (A) discontinuous at the
rationals for every r > 0; (B) continuous but
not Lipschitzian at the Liouville numbers, for
every r > 0; (C) differentiable at every irrational
algebraic number of degree <= r-1, if r > 3.
THEOREM 3: The function f^r is differentiable at every
algebraic irrational number if r > 2 (and, by
Theorem 1, at none if r <= 2).
THEOREM 4: The function f^2 is Lipschitzian but not
differentiable at the points of the set
{(1/2)*[m - sqrt(d)]: m is an integer
and there exists an integer n such that
d = m^2 - 4n is positive but not a perfect
square} . [This set is dense in the reals.]
THEOREM 5: If g is a function discontinuous at the
rationals and continuous at the irrationals,
then there is a dense uncountable subset
of the reals at each point of which g fails
to satisfy a Lipschitz condition.
つづく
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