---
OA_place: publisher
OA_type: hybrid
_id: '20008'
abstract:
- lang: eng
  text: 'We study the complexity of a class of promise graph homomorphism problems.
    For a fixed graph H, the H-colouring problem is to decide whether a given graph
    has a homomorphism to H. By a result of Hell and Nešetřil, this problem is NP-hard
    for any non-bipartite loop-less graph H. Brakensiek and Guruswami [SODA 2018]
    conjectured the hardness extends to promise graph homomorphism problems as follows:
    fix a pair of non-bipartite loop-less graphs G, H such that there is a homomorphism
    from G to H, it is NP-hard to distinguish between graphs that are G-colourable
    and those that are not H-colourable. We confirm this conjecture in the cases when
    both G and H are 4-colourable. This is a common generalisation of previous results
    of Khanna, Linial, and Safra [Comb. 20(3): 393-415 (2000)] and of Krokhin and
    Opršal [FOCS 2019]. The result is obtained by combining the algebraic approach
    to promise constraint satisfaction with methods of topological combinatorics and
    equivariant obstruction theory.'
acknowledgement: This research was supported by the Austrian Science Fund (FWF project
  P31312-N35) and by project MSCAfellow5_MUNI (CZ.02.01.01/00/22_010/0003229) financed
  by the Ministry of Education, Youth and Sports of the Czech Republic. This project
  has also received funding from the European Union’s Horizon 2020 research and innovation
  programme under the Marie Skłodowska-Curie Grant Agreement No 101034413.
article_processing_charge: Yes (in subscription journal)
author:
- first_name: Sergey
  full_name: Avvakumov, Sergey
  id: 3827DAC8-F248-11E8-B48F-1D18A9856A87
  last_name: Avvakumov
  orcid: 0000-0002-7840-5062
- first_name: Marek
  full_name: Filakovský, Marek
  id: 3E8AF77E-F248-11E8-B48F-1D18A9856A87
  last_name: Filakovský
- first_name: Jakub
  full_name: Opršal, Jakub
  id: ec596741-c539-11ec-b829-c79322a91242
  last_name: Opršal
  orcid: 0000-0003-1245-3456
- first_name: Gianluca
  full_name: Tasinato, Gianluca
  id: 0433290C-AF8F-11E9-A4C7-F729E6697425
  last_name: Tasinato
- first_name: Uli
  full_name: Wagner, Uli
  id: 36690CA2-F248-11E8-B48F-1D18A9856A87
  last_name: Wagner
  orcid: 0000-0002-1494-0568
citation:
  ama: 'Avvakumov S, Filakovský M, Opršal J, Tasinato G, Wagner U. Hardness of 4-colouring
    G-colourable graphs. In: <i>Proceedings of the 57th Annual ACM Symposium on Theory
    of Computing</i>. Association for Computing Machinery; 2025:72-83. doi:<a href="https://doi.org/10.1145/3717823.3718154">10.1145/3717823.3718154</a>'
  apa: 'Avvakumov, S., Filakovský, M., Opršal, J., Tasinato, G., &#38; Wagner, U.
    (2025). Hardness of 4-colouring G-colourable graphs. In <i>Proceedings of the
    57th Annual ACM Symposium on Theory of Computing</i> (pp. 72–83). Prague, Czechia:
    Association for Computing Machinery. <a href="https://doi.org/10.1145/3717823.3718154">https://doi.org/10.1145/3717823.3718154</a>'
  chicago: Avvakumov, Sergey, Marek Filakovský, Jakub Opršal, Gianluca Tasinato, and
    Uli Wagner. “Hardness of 4-Colouring G-Colourable Graphs.” In <i>Proceedings of
    the 57th Annual ACM Symposium on Theory of Computing</i>, 72–83. Association for
    Computing Machinery, 2025. <a href="https://doi.org/10.1145/3717823.3718154">https://doi.org/10.1145/3717823.3718154</a>.
  ieee: S. Avvakumov, M. Filakovský, J. Opršal, G. Tasinato, and U. Wagner, “Hardness
    of 4-colouring G-colourable graphs,” in <i>Proceedings of the 57th Annual ACM
    Symposium on Theory of Computing</i>, Prague, Czechia, 2025, pp. 72–83.
  ista: 'Avvakumov S, Filakovský M, Opršal J, Tasinato G, Wagner U. 2025. Hardness
    of 4-colouring G-colourable graphs. Proceedings of the 57th Annual ACM Symposium
    on Theory of Computing. STOC: Symposium on Theory of Computing, 72–83.'
  mla: Avvakumov, Sergey, et al. “Hardness of 4-Colouring G-Colourable Graphs.” <i>Proceedings
    of the 57th Annual ACM Symposium on Theory of Computing</i>, Association for Computing
    Machinery, 2025, pp. 72–83, doi:<a href="https://doi.org/10.1145/3717823.3718154">10.1145/3717823.3718154</a>.
  short: S. Avvakumov, M. Filakovský, J. Opršal, G. Tasinato, U. Wagner, in:, Proceedings
    of the 57th Annual ACM Symposium on Theory of Computing, Association for Computing
    Machinery, 2025, pp. 72–83.
conference:
  end_date: 2025-06-27
  location: Prague, Czechia
  name: 'STOC: Symposium on Theory of Computing'
  start_date: 2025-06-23
corr_author: '1'
date_created: 2025-07-13T22:01:23Z
date_published: 2025-06-15T00:00:00Z
date_updated: 2026-04-07T12:36:50Z
day: '15'
ddc:
- '000'
department:
- _id: UlWa
doi: 10.1145/3717823.3718154
ec_funded: 1
file:
- access_level: open_access
  checksum: 2c9ae7ad0102c41124976f4cb5182760
  content_type: application/pdf
  creator: dernst
  date_created: 2025-07-14T06:42:58Z
  date_updated: 2025-07-14T06:42:58Z
  file_id: '20013'
  file_name: 2025_STOC_Avvakumov.pdf
  file_size: 940827
  relation: main_file
  success: 1
file_date_updated: 2025-07-14T06:42:58Z
has_accepted_license: '1'
language:
- iso: eng
month: '06'
oa: 1
oa_version: Published Version
page: 72-83
project:
- _id: 26611F5C-B435-11E9-9278-68D0E5697425
  call_identifier: FWF
  grant_number: P31312
  name: Algorithms for Embeddings and Homotopy Theory
- _id: fc2ed2f7-9c52-11eb-aca3-c01059dda49c
  call_identifier: H2020
  grant_number: '101034413'
  name: 'IST-BRIDGE: International postdoctoral program'
publication: Proceedings of the 57th Annual ACM Symposium on Theory of Computing
publication_identifier:
  isbn:
  - '9798400715105'
  issn:
  - 0737-8017
publication_status: published
publisher: Association for Computing Machinery
quality_controlled: '1'
related_material:
  record:
  - id: '20339'
    relation: dissertation_contains
    status: public
scopus_import: '1'
status: public
title: Hardness of 4-colouring G-colourable graphs
tmp:
  image: /images/cc_by.png
  legal_code_url: https://creativecommons.org/licenses/by/4.0/legalcode
  name: Creative Commons Attribution 4.0 International Public License (CC-BY 4.0)
  short: CC BY (4.0)
type: conference
user_id: 2DF688A6-F248-11E8-B48F-1D18A9856A87
year: '2025'
...
---
_id: '15168'
abstract:
- lang: eng
  text: 'A linearly ordered (LO) k-colouring of a hypergraph is a colouring of its
    vertices with colours 1, … , k such that each edge contains a unique maximal colour.
    Deciding whether an input hypergraph admits LO k-colouring with a fixed number
    of colours is NP-complete (and in the special case of graphs, LO colouring coincides
    with the usual graph colouring). Here, we investigate the complexity of approximating
    the "linearly ordered chromatic number" of a hypergraph. We prove that the following
    promise problem is NP-complete: Given a 3-uniform hypergraph, distinguish between
    the case that it is LO 3-colourable, and the case that it is not even LO 4-colourable.
    We prove this result by a combination of algebraic, topological, and combinatorial
    methods, building on and extending a topological approach for studying approximate
    graph colouring introduced by Krokhin, Opršal, Wrochna, and Živný (2023).'
acknowledgement: "Marek Filakovský: This research was supported by Charles University
  (project PRIMUS/\r\n21/SCI/014), the Austrian Science Fund (FWF project P31312-N35),
  and MSCAfellow5_MUNI\r\n(CZ.02.01.01/00/22_010/0003229). Tamio-Vesa Nakajima: This
  research was funded by UKRI EP/X024431/1 and by a Clarendon Fund Scholarship. All
  data is provided in full in the results section of this paper. Jakub Opršal: This
  project has received funding from the European Union’s Horizon 2020 research and
  innovation programme under the Marie Skłodowska-Curie Grant Agreement No 101034413.
  Uli Wagner: This research was supported by the Austrian Science Fund (FWF project
  P31312-N35)."
alternative_title:
- LIPIcs
article_number: '34'
article_processing_charge: No
arxiv: 1
author:
- first_name: Marek
  full_name: Filakovský, Marek
  id: 3E8AF77E-F248-11E8-B48F-1D18A9856A87
  last_name: Filakovský
- first_name: Tamio Vesa
  full_name: Nakajima, Tamio Vesa
  last_name: Nakajima
- first_name: Jakub
  full_name: Opršal, Jakub
  id: ec596741-c539-11ec-b829-c79322a91242
  last_name: Opršal
  orcid: 0000-0003-1245-3456
- first_name: Gianluca
  full_name: Tasinato, Gianluca
  id: 0433290C-AF8F-11E9-A4C7-F729E6697425
  last_name: Tasinato
- first_name: Uli
  full_name: Wagner, Uli
  id: 36690CA2-F248-11E8-B48F-1D18A9856A87
  last_name: Wagner
  orcid: 0000-0002-1494-0568
citation:
  ama: 'Filakovský M, Nakajima TV, Opršal J, Tasinato G, Wagner U. Hardness of linearly
    ordered 4-colouring of 3-colourable 3-uniform hypergraphs. In: <i>41st International
    Symposium on Theoretical Aspects of Computer Science</i>. Vol 289. Schloss Dagstuhl
    - Leibniz-Zentrum für Informatik; 2024. doi:<a href="https://doi.org/10.4230/LIPIcs.STACS.2024.34">10.4230/LIPIcs.STACS.2024.34</a>'
  apa: 'Filakovský, M., Nakajima, T. V., Opršal, J., Tasinato, G., &#38; Wagner, U.
    (2024). Hardness of linearly ordered 4-colouring of 3-colourable 3-uniform hypergraphs.
    In <i>41st International Symposium on Theoretical Aspects of Computer Science</i>
    (Vol. 289). Clermont-Ferrand, France: Schloss Dagstuhl - Leibniz-Zentrum für Informatik.
    <a href="https://doi.org/10.4230/LIPIcs.STACS.2024.34">https://doi.org/10.4230/LIPIcs.STACS.2024.34</a>'
  chicago: Filakovský, Marek, Tamio Vesa Nakajima, Jakub Opršal, Gianluca Tasinato,
    and Uli Wagner. “Hardness of Linearly Ordered 4-Colouring of 3-Colourable 3-Uniform
    Hypergraphs.” In <i>41st International Symposium on Theoretical Aspects of Computer
    Science</i>, Vol. 289. Schloss Dagstuhl - Leibniz-Zentrum für Informatik, 2024.
    <a href="https://doi.org/10.4230/LIPIcs.STACS.2024.34">https://doi.org/10.4230/LIPIcs.STACS.2024.34</a>.
  ieee: M. Filakovský, T. V. Nakajima, J. Opršal, G. Tasinato, and U. Wagner, “Hardness
    of linearly ordered 4-colouring of 3-colourable 3-uniform hypergraphs,” in <i>41st
    International Symposium on Theoretical Aspects of Computer Science</i>, Clermont-Ferrand,
    France, 2024, vol. 289.
  ista: 'Filakovský M, Nakajima TV, Opršal J, Tasinato G, Wagner U. 2024. Hardness
    of linearly ordered 4-colouring of 3-colourable 3-uniform hypergraphs. 41st International
    Symposium on Theoretical Aspects of Computer Science. STACS: Symposium on Theoretical
    Aspects of Computer Science, LIPIcs, vol. 289, 34.'
  mla: Filakovský, Marek, et al. “Hardness of Linearly Ordered 4-Colouring of 3-Colourable
    3-Uniform Hypergraphs.” <i>41st International Symposium on Theoretical Aspects
    of Computer Science</i>, vol. 289, 34, Schloss Dagstuhl - Leibniz-Zentrum für
    Informatik, 2024, doi:<a href="https://doi.org/10.4230/LIPIcs.STACS.2024.34">10.4230/LIPIcs.STACS.2024.34</a>.
  short: M. Filakovský, T.V. Nakajima, J. Opršal, G. Tasinato, U. Wagner, in:, 41st
    International Symposium on Theoretical Aspects of Computer Science, Schloss Dagstuhl
    - Leibniz-Zentrum für Informatik, 2024.
conference:
  end_date: 2024-03-14
  location: Clermont-Ferrand, France
  name: 'STACS: Symposium on Theoretical Aspects of Computer Science'
  start_date: 2024-03-12
corr_author: '1'
date_created: 2024-03-24T23:00:59Z
date_published: 2024-03-01T00:00:00Z
date_updated: 2026-04-07T12:36:50Z
day: '01'
ddc:
- '510'
department:
- _id: UlWa
doi: 10.4230/LIPIcs.STACS.2024.34
ec_funded: 1
external_id:
  arxiv:
  - '2312.12981'
  isi:
  - '001300393400034'
file:
- access_level: open_access
  checksum: 0524d4189fd1ed08989546511343edf3
  content_type: application/pdf
  creator: dernst
  date_created: 2024-03-25T07:44:30Z
  date_updated: 2024-03-25T07:44:30Z
  file_id: '15175'
  file_name: 2024_LIPICs_Filakovsky.pdf
  file_size: 927290
  relation: main_file
  success: 1
file_date_updated: 2024-03-25T07:44:30Z
has_accepted_license: '1'
intvolume: '       289'
isi: 1
language:
- iso: eng
month: '03'
oa: 1
oa_version: Published Version
project:
- _id: 26611F5C-B435-11E9-9278-68D0E5697425
  call_identifier: FWF
  grant_number: P31312
  name: Algorithms for Embeddings and Homotopy Theory
- _id: fc2ed2f7-9c52-11eb-aca3-c01059dda49c
  call_identifier: H2020
  grant_number: '101034413'
  name: 'IST-BRIDGE: International postdoctoral program'
publication: 41st International Symposium on Theoretical Aspects of Computer Science
publication_identifier:
  eissn:
  - 1868-8969
  isbn:
  - '9783959773119'
publication_status: published
publisher: Schloss Dagstuhl - Leibniz-Zentrum für Informatik
quality_controlled: '1'
related_material:
  record:
  - id: '20339'
    relation: dissertation_contains
    status: public
scopus_import: '1'
status: public
title: Hardness of linearly ordered 4-colouring of 3-colourable 3-uniform hypergraphs
tmp:
  image: /images/cc_by.png
  legal_code_url: https://creativecommons.org/licenses/by/4.0/legalcode
  name: Creative Commons Attribution 4.0 International Public License (CC-BY 4.0)
  short: CC BY (4.0)
type: conference
user_id: 317138e5-6ab7-11ef-aa6d-ffef3953e345
volume: 289
year: '2024'
...
---
_id: '7806'
abstract:
- lang: eng
  text: "We consider the following decision problem EMBEDk→d in computational topology
    (where k ≤ d are fixed positive integers): Given a finite simplicial complex K
    of dimension k, does there exist a (piecewise-linear) embedding of K into ℝd?\r\nThe
    special case EMBED1→2 is graph planarity, which is decidable in linear time, as
    shown by Hopcroft and Tarjan. In higher dimensions, EMBED2→3 and EMBED3→3 are
    known to be decidable (as well as NP-hard), and recent results of Čadek et al.
    in computational homotopy theory, in combination with the classical Haefliger–Weber
    theorem in geometric topology, imply that EMBEDk→d can be solved in polynomial
    time for any fixed pair (k, d) of dimensions in the so-called metastable range
    .\r\nHere, by contrast, we prove that EMBEDk→d is algorithmically undecidable
    for almost all pairs of dimensions outside the metastable range, namely for .
    This almost completely resolves the decidability vs. undecidability of EMBEDk→d
    in higher dimensions and establishes a sharp dichotomy between polynomial-time
    solvability and undecidability.\r\nOur result complements (and in a wide range
    of dimensions strengthens) earlier results of Matoušek, Tancer, and the second
    author, who showed that EMBEDk→d is undecidable for 4 ≤ k ϵ {d – 1, d}, and NP-hard
    for all remaining pairs (k, d) outside the metastable range and satisfying d ≥
    4."
article_processing_charge: No
author:
- first_name: Marek
  full_name: Filakovský, Marek
  id: 3E8AF77E-F248-11E8-B48F-1D18A9856A87
  last_name: Filakovský
- first_name: Uli
  full_name: Wagner, Uli
  id: 36690CA2-F248-11E8-B48F-1D18A9856A87
  last_name: Wagner
  orcid: 0000-0002-1494-0568
- first_name: Stephan Y
  full_name: Zhechev, Stephan Y
  id: 3AA52972-F248-11E8-B48F-1D18A9856A87
  last_name: Zhechev
citation:
  ama: 'Filakovský M, Wagner U, Zhechev SY. Embeddability of simplicial complexes
    is undecidable. In: <i>Proceedings of the Annual ACM-SIAM Symposium on Discrete
    Algorithms</i>. Vol 2020-January. SIAM; 2020:767-785. doi:<a href="https://doi.org/10.1137/1.9781611975994.47">10.1137/1.9781611975994.47</a>'
  apa: 'Filakovský, M., Wagner, U., &#38; Zhechev, S. Y. (2020). Embeddability of
    simplicial complexes is undecidable. In <i>Proceedings of the Annual ACM-SIAM
    Symposium on Discrete Algorithms</i> (Vol. 2020–January, pp. 767–785). Salt Lake
    City, UT, United States: SIAM. <a href="https://doi.org/10.1137/1.9781611975994.47">https://doi.org/10.1137/1.9781611975994.47</a>'
  chicago: Filakovský, Marek, Uli Wagner, and Stephan Y Zhechev. “Embeddability of
    Simplicial Complexes Is Undecidable.” In <i>Proceedings of the Annual ACM-SIAM
    Symposium on Discrete Algorithms</i>, 2020–January:767–85. SIAM, 2020. <a href="https://doi.org/10.1137/1.9781611975994.47">https://doi.org/10.1137/1.9781611975994.47</a>.
  ieee: M. Filakovský, U. Wagner, and S. Y. Zhechev, “Embeddability of simplicial
    complexes is undecidable,” in <i>Proceedings of the Annual ACM-SIAM Symposium
    on Discrete Algorithms</i>, Salt Lake City, UT, United States, 2020, vol. 2020–January,
    pp. 767–785.
  ista: 'Filakovský M, Wagner U, Zhechev SY. 2020. Embeddability of simplicial complexes
    is undecidable. Proceedings of the Annual ACM-SIAM Symposium on Discrete Algorithms.
    SODA: Symposium on Discrete Algorithms vol. 2020–January, 767–785.'
  mla: Filakovský, Marek, et al. “Embeddability of Simplicial Complexes Is Undecidable.”
    <i>Proceedings of the Annual ACM-SIAM Symposium on Discrete Algorithms</i>, vol.
    2020–January, SIAM, 2020, pp. 767–85, doi:<a href="https://doi.org/10.1137/1.9781611975994.47">10.1137/1.9781611975994.47</a>.
  short: M. Filakovský, U. Wagner, S.Y. Zhechev, in:, Proceedings of the Annual ACM-SIAM
    Symposium on Discrete Algorithms, SIAM, 2020, pp. 767–785.
conference:
  end_date: 2020-01-08
  location: Salt Lake City, UT, United States
  name: 'SODA: Symposium on Discrete Algorithms'
  start_date: 2020-01-05
date_created: 2020-05-10T22:00:48Z
date_published: 2020-01-01T00:00:00Z
date_updated: 2021-01-12T08:15:38Z
day: '01'
department:
- _id: UlWa
doi: 10.1137/1.9781611975994.47
language:
- iso: eng
main_file_link:
- open_access: '1'
  url: https://doi.org/10.1137/1.9781611975994.47
month: '01'
oa: 1
oa_version: Published Version
page: 767-785
project:
- _id: 26611F5C-B435-11E9-9278-68D0E5697425
  call_identifier: FWF
  grant_number: P31312
  name: Algorithms for Embeddings and Homotopy Theory
publication: Proceedings of the Annual ACM-SIAM Symposium on Discrete Algorithms
publication_identifier:
  isbn:
  - '9781611975994'
publication_status: published
publisher: SIAM
quality_controlled: '1'
scopus_import: 1
status: public
title: Embeddability of simplicial complexes is undecidable
type: conference
user_id: 2DF688A6-F248-11E8-B48F-1D18A9856A87
volume: 2020-January
year: '2020'
...
---
_id: '6563'
abstract:
- lang: eng
  text: "This paper presents two algorithms. The first decides the existence of a
    pointed homotopy between given simplicial maps \U0001D453,\U0001D454:\U0001D44B→\U0001D44C,
    and the second computes the group [\U0001D6F4\U0001D44B,\U0001D44C]∗ of pointed
    homotopy classes of maps from a suspension; in both cases, the target Y is assumed
    simply connected. More generally, these algorithms work relative to \U0001D434⊆\U0001D44B."
article_processing_charge: No
article_type: original
arxiv: 1
author:
- first_name: Marek
  full_name: Filakovský, Marek
  id: 3E8AF77E-F248-11E8-B48F-1D18A9856A87
  last_name: Filakovský
- first_name: Lukas
  full_name: Vokřínek, Lukas
  last_name: Vokřínek
citation:
  ama: Filakovský M, Vokřínek L. Are two given maps homotopic? An algorithmic viewpoint.
    <i>Foundations of Computational Mathematics</i>. 2020;20:311-330. doi:<a href="https://doi.org/10.1007/s10208-019-09419-x">10.1007/s10208-019-09419-x</a>
  apa: Filakovský, M., &#38; Vokřínek, L. (2020). Are two given maps homotopic? An
    algorithmic viewpoint. <i>Foundations of Computational Mathematics</i>. Springer
    Nature. <a href="https://doi.org/10.1007/s10208-019-09419-x">https://doi.org/10.1007/s10208-019-09419-x</a>
  chicago: Filakovský, Marek, and Lukas Vokřínek. “Are Two given Maps Homotopic? An
    Algorithmic Viewpoint.” <i>Foundations of Computational Mathematics</i>. Springer
    Nature, 2020. <a href="https://doi.org/10.1007/s10208-019-09419-x">https://doi.org/10.1007/s10208-019-09419-x</a>.
  ieee: M. Filakovský and L. Vokřínek, “Are two given maps homotopic? An algorithmic
    viewpoint,” <i>Foundations of Computational Mathematics</i>, vol. 20. Springer
    Nature, pp. 311–330, 2020.
  ista: Filakovský M, Vokřínek L. 2020. Are two given maps homotopic? An algorithmic
    viewpoint. Foundations of Computational Mathematics. 20, 311–330.
  mla: Filakovský, Marek, and Lukas Vokřínek. “Are Two given Maps Homotopic? An Algorithmic
    Viewpoint.” <i>Foundations of Computational Mathematics</i>, vol. 20, Springer
    Nature, 2020, pp. 311–30, doi:<a href="https://doi.org/10.1007/s10208-019-09419-x">10.1007/s10208-019-09419-x</a>.
  short: M. Filakovský, L. Vokřínek, Foundations of Computational Mathematics 20 (2020)
    311–330.
date_created: 2019-06-16T21:59:14Z
date_published: 2020-04-01T00:00:00Z
date_updated: 2025-07-10T11:53:32Z
day: '01'
department:
- _id: UlWa
doi: 10.1007/s10208-019-09419-x
external_id:
  arxiv:
  - '1312.2337'
  isi:
  - '000522437400004'
intvolume: '        20'
isi: 1
language:
- iso: eng
main_file_link:
- open_access: '1'
  url: https://arxiv.org/abs/1312.2337
month: '04'
oa: 1
oa_version: Preprint
page: 311-330
project:
- _id: 26611F5C-B435-11E9-9278-68D0E5697425
  call_identifier: FWF
  grant_number: P31312
  name: Algorithms for Embeddings and Homotopy Theory
publication: Foundations of Computational Mathematics
publication_identifier:
  eissn:
  - 1615-3383
  issn:
  - 1615-3375
publication_status: published
publisher: Springer Nature
quality_controlled: '1'
scopus_import: '1'
status: public
title: Are two given maps homotopic? An algorithmic viewpoint
type: journal_article
user_id: 2DF688A6-F248-11E8-B48F-1D18A9856A87
volume: 20
year: '2020'
...
---
_id: '6774'
abstract:
- lang: eng
  text: "A central problem of algebraic topology is to understand the homotopy groups
    \ \U0001D70B\U0001D451(\U0001D44B)  of a topological space X. For the computational
    version of the problem, it is well known that there is no algorithm to decide
    whether the fundamental group  \U0001D70B1(\U0001D44B)  of a given finite simplicial
    complex X is trivial. On the other hand, there are several algorithms that, given
    a finite simplicial complex X that is simply connected (i.e., with   \U0001D70B1(\U0001D44B)
    \ trivial), compute the higher homotopy group   \U0001D70B\U0001D451(\U0001D44B)
    \ for any given   \U0001D451≥2 . However, these algorithms come with a caveat:
    They compute the isomorphism type of   \U0001D70B\U0001D451(\U0001D44B) ,   \U0001D451≥2
    \ as an abstract finitely generated abelian group given by generators and relations,
    but they work with very implicit representations of the elements of   \U0001D70B\U0001D451(\U0001D44B)
    . Converting elements of this abstract group into explicit geometric maps from
    the d-dimensional sphere   \U0001D446\U0001D451  to X has been one of the main
    unsolved problems in the emerging field of computational homotopy theory. Here
    we present an algorithm that, given a simply connected space X, computes   \U0001D70B\U0001D451(\U0001D44B)
    \ and represents its elements as simplicial maps from a suitable triangulation
    of the d-sphere   \U0001D446\U0001D451  to X. For fixed d, the algorithm runs
    in time exponential in   size(\U0001D44B) , the number of simplices of X. Moreover,
    we prove that this is optimal: For every fixed   \U0001D451≥2 , we construct a
    family of simply connected spaces X such that for any simplicial map representing
    a generator of   \U0001D70B\U0001D451(\U0001D44B) , the size of the triangulation
    of   \U0001D446\U0001D451  on which the map is defined, is exponential in size(\U0001D44B)
    ."
article_type: original
author:
- first_name: Marek
  full_name: Filakovský, Marek
  id: 3E8AF77E-F248-11E8-B48F-1D18A9856A87
  last_name: Filakovský
- first_name: Peter
  full_name: Franek, Peter
  id: 473294AE-F248-11E8-B48F-1D18A9856A87
  last_name: Franek
  orcid: 0000-0001-8878-8397
- first_name: Uli
  full_name: Wagner, Uli
  id: 36690CA2-F248-11E8-B48F-1D18A9856A87
  last_name: Wagner
  orcid: 0000-0002-1494-0568
- first_name: Stephan Y
  full_name: Zhechev, Stephan Y
  id: 3AA52972-F248-11E8-B48F-1D18A9856A87
  last_name: Zhechev
citation:
  ama: Filakovský M, Franek P, Wagner U, Zhechev SY. Computing simplicial representatives
    of homotopy group elements. <i>Journal of Applied and Computational Topology</i>.
    2018;2(3-4):177-231. doi:<a href="https://doi.org/10.1007/s41468-018-0021-5">10.1007/s41468-018-0021-5</a>
  apa: Filakovský, M., Franek, P., Wagner, U., &#38; Zhechev, S. Y. (2018). Computing
    simplicial representatives of homotopy group elements. <i>Journal of Applied and
    Computational Topology</i>. Springer. <a href="https://doi.org/10.1007/s41468-018-0021-5">https://doi.org/10.1007/s41468-018-0021-5</a>
  chicago: Filakovský, Marek, Peter Franek, Uli Wagner, and Stephan Y Zhechev. “Computing
    Simplicial Representatives of Homotopy Group Elements.” <i>Journal of Applied
    and Computational Topology</i>. Springer, 2018. <a href="https://doi.org/10.1007/s41468-018-0021-5">https://doi.org/10.1007/s41468-018-0021-5</a>.
  ieee: M. Filakovský, P. Franek, U. Wagner, and S. Y. Zhechev, “Computing simplicial
    representatives of homotopy group elements,” <i>Journal of Applied and Computational
    Topology</i>, vol. 2, no. 3–4. Springer, pp. 177–231, 2018.
  ista: Filakovský M, Franek P, Wagner U, Zhechev SY. 2018. Computing simplicial representatives
    of homotopy group elements. Journal of Applied and Computational Topology. 2(3–4),
    177–231.
  mla: Filakovský, Marek, et al. “Computing Simplicial Representatives of Homotopy
    Group Elements.” <i>Journal of Applied and Computational Topology</i>, vol. 2,
    no. 3–4, Springer, 2018, pp. 177–231, doi:<a href="https://doi.org/10.1007/s41468-018-0021-5">10.1007/s41468-018-0021-5</a>.
  short: M. Filakovský, P. Franek, U. Wagner, S.Y. Zhechev, Journal of Applied and
    Computational Topology 2 (2018) 177–231.
corr_author: '1'
date_created: 2019-08-08T06:47:40Z
date_published: 2018-12-01T00:00:00Z
date_updated: 2026-04-08T13:56:01Z
day: '01'
ddc:
- '514'
department:
- _id: UlWa
doi: 10.1007/s41468-018-0021-5
file:
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  date_updated: 2020-07-14T12:47:40Z
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file_date_updated: 2020-07-14T12:47:40Z
has_accepted_license: '1'
intvolume: '         2'
issue: 3-4
language:
- iso: eng
month: '12'
oa: 1
oa_version: Published Version
page: 177-231
project:
- _id: 25F8B9BC-B435-11E9-9278-68D0E5697425
  call_identifier: FWF
  grant_number: M01980
  name: Robust Invariants of Nonlinear Systems
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  call_identifier: FWF
  name: FWF Open Access Fund
publication: Journal of Applied and Computational Topology
publication_identifier:
  eissn:
  - 2367-1734
  issn:
  - 2367-1726
publication_status: published
publisher: Springer
quality_controlled: '1'
related_material:
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  - id: '6681'
    relation: dissertation_contains
    status: public
scopus_import: '1'
status: public
title: Computing simplicial representatives of homotopy group elements
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  image: /images/cc_by.png
  legal_code_url: https://creativecommons.org/licenses/by/4.0/legalcode
  name: Creative Commons Attribution 4.0 International Public License (CC-BY 4.0)
  short: CC BY (4.0)
type: journal_article
user_id: 2DF688A6-F248-11E8-B48F-1D18A9856A87
volume: 2
year: '2018'
...
