LIE GROUP ANALYSIS CCLLAASSSSIICCAALL HHEERRIITTAAGGEE Edited by Nail H. Ibragimov ALGA Publications LIE GROUP ANALYSIS CLASSICAL HERITAGE Edited by Nail H. Ibragimov Translated by Nail H. Ibragimov Elena D. Ishmakova Roza M. Yakushina ALGA Publications Blekinge Institute of Technology Karlskrona, Sweden c 2004 Nail H. Ibragimov e-mail:°
[email protected] http://www.bth.se/alga All rights reserved. No part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording, scanning or otherwise, without written permission of the editor. The cover illustration: An example of invariant surfaces Sophus Lie, "Lectures on transformation groups", 1893, p. 414 ISBN 91-7295-996-7 Preface Today, acquaintance with modern group analysis and its classical founda- tions becomes an important part of mathematical culture of anyone con- structing and investigating mathematical models. However, many of clas- sical works in Lie group analysis, e.g. important papers of S.Lie and A.V.BÄacklund written in German and some fundamental papers of L.V. Ovsyannikov written in Russian have been not translated into English till now. The present small collection o®ers an English translation of four fun- damental papers by these authors. I have selected here some of my favorite papers containing profound re- sults signi¯cant for modern group analysis. The ¯rst paper imparts not only Lie's interesting view on the development of the general theory of di®eren- tial equations but also contains Lie's theory of group invariant solutions. His second paper is dedicated to group classi¯cation of second-order linear partial di®erential equations in two variables and can serve as a concise prac- tical guide to the group analysis of partial di®erential equations even today.