**News**

23 Feb 2015, the slide file was uploaded

**Title**

The randomness hierarchy and reducibilities as its refinements

**Type**

Joint seminar at TMU (in Japanese)

**Download**

TMU-slide in Japanese

宮部賢志（ミヤベケンシ）

**News**

23 Feb 2015, the slide file was uploaded

**Title**

The randomness hierarchy and reducibilities as its refinements

**Type**

Joint seminar at TMU (in Japanese)

**Download**

TMU-slide in Japanese

Posted in Talks
Leave a comment

**News**

4 Jan 2015, the slide file was uploaded

**Title**

Total-machine reducibility and randomness notions

**Type**

Asian Logic Conference 2015

**Download**

slide

Posted in Talks
Leave a comment

**News**

19 Jan 2014, submitted

**Title**

Unified Characterizations of Lowness Properties via Kolmogorov Complexity

(with T. Kihara)

**Type**

Full paper

**Journal**

Archive for Mathematical Logic

DOI: 10.1007/s00153-014-0413-8

**Abstract**

Consider a randomness notion $\mathcal C$.

A uniform test in the sense of $\mathcal C$ is a total computable procedure that each oracle $X$ produces a test relative to $X$ in the sense of $\mathcal C$.

We say that a binary sequence $Y$ is $\mathcal C$-random uniformly relative to $X$ if $Y$ passes all uniform $\mathcal C$ tests relative to $X$.

Suppose now we have a pair of randomness notions $\mathcal C$ and $\mathcal D$ where $\mathcal{C}\subseteq \mathcal{D}$, for instance Martin-L\”of randomness and Schnorr randomness. Several authors have characterized classes of the form Low($\mathcal C, \mathcal D$) which consist of the oracles $X$ that are so feeble that $\mathcal C \subseteq \mathcal D^X$. Our goal is to do the same when the randomness notion $\mathcal D$ is relativized uniformly: denote by Low$^\star$($\mathcal C, \mathcal D$) the class of oracles $X$ such that every $\mathcal C$-random is uniformly $\mathcal D$-random relative to $X$.

(1) We show that $X\in{\rm Low}^\star({\rm MLR},{\rm SR})$ if and only if $X$ is c.e.~tt-traceable if and only if $X$ is anticomplex if and only if $X$ is Martin-L\”of packing measure zero with respect to all computable dimension functions.

(2) We also show that $X\in{\rm Low}^\star({\rm SR},{\rm WR})$ if and only if $X$ is computably i.o.~tt-traceable if and only if $X$ is not totally complex if and only if $X$ is Schnorr Hausdorff measure zero with respect to all computable dimension functions.

**Download**

preprint

Posted in Publication
Leave a comment

**News**

13 Nov 2014, the slide file was uploaded

**Title**

Derandomization in game-theoretic probability

**Type**

GTP 2014: Fifth Workshop on Game-Theoretic Probability and Related Topics

**Download**

miyabe-gtp2014

Posted in Talks
Leave a comment

**News**

3 Nov 2014. Submitted

**Title**

Using Almost-Everywhere Theorems from Analysis to Study Randomness

(with Jing Zhang and Andre Nies)

**Type**

Full paper

**Journal**

Submitted

arXiv

**Abstract**

We study algorithmic randomness notions via effective versions of almost-everywhere theorems from analysis and ergodic theory. The effectivization is in terms of objects described by a computably enumerable set, such as lower semicomputable functions. The corresponding randomness notions are slightly stronger than Martin-Lo ̈f (ML) randomness. We establish several equivalences. Given a ML-random real z, the additional randomness strengths needed for the following are equivalent.

(1) all effectively closed classes containing z have density 1 at z.

(2) all nondecreasing functions with uniformly left-c.e. increments are differentiable at z.

(3) z is a Lebesgue point of each lower semicomputable integrable function.

We also consider convergence of left-c.e. martingales, and convergence in the sense of Birkhoff’s pointwise ergodic theorem. Lastly we study randomness notions for density of $\Pi^0_n$ and $\Sigma^1_1$ classes.

Posted in Publication
Leave a comment

An article was published in Mathematical Seminar Oct 2014.

Posted in Publication
Leave a comment

Posted in Diary
Leave a comment

**News**

17 Aug 2014, the slide file was uploaded

**Title**

Betting game and mathematics

**Type**

Summer Seminar of Meiji University for high school students

**Download**

miyabe-summer-seminar-2014

Posted in Talks
Leave a comment

**News**

27 Sep 2014, Online

3 Aug 2014, Accepted in SPA

12 Feb 2014. Submitted

**Title**

Derandomization in Game-Theoretic Probability

(with A. Takemura)

**Type**

Full paper

**Journal**

Stochastic Processes and their Applications 125, 39-59, 2015

**Abstract**

We give a general method for constructing a deterministic strategy

of Reality from a randomized strategy in game-theoretic probability.

The construction can be seen as derandomization in game-theoretic probability.

**Download**

preprint

Posted in Publication
Leave a comment

**News**

19 June 2014, the slide file was uploaded

13 June 2014, the talk was given

**Title**

Schnorr randomness versions of K, C, LR, vL-reducibilities

**Type**

Conference on Computability, Complexity and Randomness CCR 2014

**Download**

miyabe-ccr2014

Posted in Talks
Leave a comment