Web page of Ryoko Oishi-Tomiyasu

Our research theme is to develop algorithms and applications for discrete structures such as lattices, rings of integers, and point configurations on Euclidean spaces and manifolds, by using tools and theories of geometry of numbers, algebraic number theory, discrete mathematics, convex optimization, and analytical methods related to quadratic forms and diffraction theory of crystals and quasicrystals.


  • 2022/2Other
    I've returned to work after a maternity leave.
  • 2022/09/09Talk
    "Reduction theory for unit-cell parameters containing observation errors", satellite of the 33rd European Crystallographic Meeting.
  • 2022/05/26Talk
    "Reduction theory for determining the Bravais type of unit-cell parameters containing observation errors", MIF++ seminar, University of Liverpool, UK(online).
  • 2023/03/28Paper
    "Universal sums of generalized heptagonal numbers" (partially supported by SENTAN-Q program and coauthored with the program mentor and student). arxiv(submitted)
  • 2022/02/25Talk
    "Aperiodic packing construction derived from phyllotaxis", Workshop "Number theory and Ergodic theory"(online)
  • 2021/08/16Talk
    "Global optimization of magnetic structure analysis by semidefinite relaxation method " (Joint work with Nissan Arc, ltd. and Powder software group of KEK), MS-22: Methods and software developments for magnetic-structure analysis, IUCr25. slides
  • 2021/06/28Paper
    "Packing theory derived from phyllotaxis and products of linear forms" (Joint work conducted as part of the SENTAN-Q program with Mr. Graiff Zurita and Prof. Kane of HKU). arxiv(submitted)
  • 2021/06/18Talk
    "Application of geometry of numbers to problems in the real world ", SNU-KYUSHU Workshop in Number Theory.
  • 2021/03/31Paper
    "Distribution rules of systematic absences and generalized de Wolff figures of merit applied to electron backscatter diffraction ab initio indexing" accepted by J. Appl. Cryst.
    (web, arxiv, Joint work with Nippon Steel Corp.)


Institute of Mathematics for Industry, Kyushu UniversityProfessor  Ryoko Tomiyasu

  • History
    2008 Research fellow IMSS, KEK → 2010 Ph.D of Mathematical Sciences (Supervised by Prof. Takayuki Oda of The University of Tokyo) → 2011 Assistant Professor IMSS, KEK → 2015 JST PRESTO Researcher (Nishiura lab of AIMR, Tohoku University) → 2016 Associated Professor, Yamagata University → 2019 Associated Professor, Kyushu University.
  • Expertise
    Applied algebra, Number theory, Mathematical crystallography
    I'm interested in algebra, discrete mathematics and number theory, and using them to solve various problems in nature.

    My projects are supported by the following grants:

    Grant-in-Aid for Scientific Research (C):“Study on discrete point sets to produce new applications of lattice theory and algebraic computation.”
    JST FOREST:“Discrete modeling with a new biological-origin method for packing and mesh generation.”
  • Multidisciplinary research
    I have been collaborating with the scientific community for many years, in order to find new mathematical problems. Software development works as a useful communication tool for this. I've also published papers based on mathematics including number theory(e.g., ambiguities in lattice determination), in response to the scientific community's need.

Web pages about my research outside the university

Distributed Software

Open Source (The methods are described in the articles)

  1. EBSD ab-initio indexing software EBSD-CONOGRAPH CUI version (C++)

The following are cited in International Tables Vol. H (volume of powder diffraction)

  1. Powder autoindexing software Conograph CUI version (C++, OpenMP)
  2. Error-stable Bravais lattice determination program in CONOGRAPH (C++)
  3. Peak search program in CONOGRAPH (C++)

Software for J-PARC users

  1. Powder autoindexing software Conograph
  2. Rietveld analysis software (open source; Z-Rietveld code belongs to KEK as intellectual property. Please contact us if you want to use it.)

Copyright © Ryoko Tomiyasu All Rights Reserved.