Krupka, Demeter The Sonin-Douglas problem. (English) Zbl 1337.49063 Zenkov, Dmitry V. (ed.), The inverse problem of the calculus of variations. Local and global theory. Amsterdam: Atlantis Press (ISBN 978-94-6239-108-6/hbk; 978-94-6239-109-3/ebook). Atlantis Studies in Variational Geometry 2, 31-73 (2015). MSC: 49N45 PDFBibTeX XMLCite \textit{D. Krupka}, Atlantis Stud. Var. Geom. 2, 31--73 (2015; Zbl 1337.49063) Full Text: DOI
Bloch, Anthony M.; Krupka, Demeter; Zenkov, Dmitry V. The Helmholtz conditions and the method of controlled Lagrangians. (English) Zbl 1337.49062 Zenkov, Dmitry V. (ed.), The inverse problem of the calculus of variations. Local and global theory. Amsterdam: Atlantis Press (ISBN 978-94-6239-108-6/hbk; 978-94-6239-109-3/ebook). Atlantis Studies in Variational Geometry 2, 1-29 (2015). MSC: 49N45 93B52 93D15 PDFBibTeX XMLCite \textit{A. M. Bloch} et al., Atlantis Stud. Var. Geom. 2, 1--29 (2015; Zbl 1337.49062) Full Text: DOI
Krupka, Demeter; Krupková, Olga; Prince, Geoff; Sarlet, Willy Contact symmetries of the Helmholtz form. (English) Zbl 1354.58012 Differ. Geom. Appl. 25, No. 5, 518-542 (2007). MSC: 58E30 49S05 58A15 58A20 PDFBibTeX XMLCite \textit{D. Krupka} et al., Differ. Geom. Appl. 25, No. 5, 518--542 (2007; Zbl 1354.58012) Full Text: DOI