A finite group of order n can be represented by its Cayley table. In the word-RAM model the Cayley table of a group of order n can be stored using O(n²) words and can be used to answer a multiplication query in constant time. It is interesting to ask if we can design a data structure to store a group of order n that uses o(n²) space but can still answer a multiplication query in constant time. We design a constant query-time data structure that can store any finite group using O(n) words where n is the order of the group. Farzan and Munro (ISSAC 2006) gave an information theoretic lower bound of Ω(n) on the number of words to store a group of order n. Since our data structure achieves this lower bound and answers queries in constant time, it is optimal in both space usage and query-time. A crucial step in the process is essentially to design linear space and constant query-time data structures for nonabelian simple groups. The data structures for nonableian simple groups are designed using a lemma that we prove using the Classification Theorem for Finite Simple Groups (CFSG).
@InProceedings{das_et_al:LIPIcs.STACS.2022.25, author = {Das, Bireswar and Kumar, Anant and Sharma, Shivdutt and Thakkar, Dhara}, title = {{Linear Space Data Structures for Finite Groups with Constant Query-Time}}, booktitle = {39th International Symposium on Theoretical Aspects of Computer Science (STACS 2022)}, pages = {25:1--25:17}, series = {Leibniz International Proceedings in Informatics (LIPIcs)}, ISBN = {978-3-95977-222-8}, ISSN = {1868-8969}, year = {2022}, volume = {219}, editor = {Berenbrink, Petra and Monmege, Benjamin}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.STACS.2022.25}, URN = {urn:nbn:de:0030-drops-158350}, doi = {10.4230/LIPIcs.STACS.2022.25}, annote = {Keywords: Compact Data Structures, Space Efficient Representations, Finite Groups, Simple Groups, Classification Theorem for Finite Simple Groups} }
Feedback for Dagstuhl Publishing