The paper gives an overview on convex sets and starshaped sets in Carnot groups and in the more general case of geometries of vector fields, including in particular the Hoermander case. We develop some new notions and investigate their mutual relations and properties.

Contact details are reproduced from the original publication and may be historical.

  1. Z. Balogh, M. Rickly: Regularity of convex functions on Heisenberg groups, Ann. Sc. Norm. Super. Pisa Cl. Sci. (5), 2(4) (2003) 847–868.Google Scholar
  2. M. Bardi, I. Capuzzo Dolcetta: Optimal Control and Viscosity Solutions of Hamilton-Jacobi-Bellman Equations, Birkhäuser, Boston (1997).https://doi.org/10.1007/978-0-8176-4755-1Google Scholar
  3. M. Bardi, F. Dragoni: Convexity and semiconvexity along vector fields, Calc. Var. Partial Differential Equations 42(3-4) (2011) 405–427.https://doi.org/10.1007/s00526-011-0392-0Google Scholar
  4. M. Bardi, F. Dragoni: Subdifferential and properties of convex functions with respect to vector fields, J. Convex Analysis 21(3) (2014) 785–810.https://doi.org/10.68381/jca21042Google Scholar
  5. A. Bellaïche, J. J. Risler (eds.): Sub-Riemannian Geometry, Progress in Mathematics 144, Birkhäuser, Basel (1996).https://doi.org/10.1007/978-3-0348-9210-0Google Scholar
  6. A. Bonfiglioli, E. Lanconelli, F. Uguzzoni: Stratified Lie Groups and Potential Theory for Their Sub-Laplacians, Springer, Berlin (2007).Google Scholar
  7. A. Calogero, G. Carcano, R. Pini: Twisted Convex Hulls in the Heisenberg Group, J. Convex Analysis 14(3) (2007) 607–619.https://doi.org/10.68381/jca14036Google Scholar
  8. D. Danielli, N. Garofalo: Geometric properties of solutions to subelliptic equations in nilpotent Lie groups, in: Reaction Diffusion Systems (Trieste, 1995), Lecture Notes Pure Appl. Math. 194, Dekker, New York (1998) 89–105.https://doi.org/10.1201/9781003072195-9Google Scholar
  9. D. Danielli, N. Garofalo: Green functions in Carnot groups and the geometry of their level sets, in preparation.Google Scholar
  10. D. Danielli, N. Garofalo, D. M. Nhieu: Notions of convexity in Carnot groups, Comm. Anal. Geom. 11(2) (2003) 263–341.https://doi.org/10.4310/CAG.2003.v11.n2.a5Google Scholar
  11. D. Danielli, N. Garofalo, D. M. Nhieu, F. Tournier: The theorem of Busemann-Feller-Alexandrov in Carnot groups, Comm. Anal. Geom. 12(4) (2004) 853–886.https://doi.org/10.4310/CAG.2004.v12.n4.a5Google Scholar
  12. F. Dragoni, N. Garofalo, P. Salani: Starshapedeness for level sets of nonlinear subelliptic PDEs, Journal of the LMS 2 (2018) 1–18.Google Scholar
  13. D. Filali: Starshapedness and Convexity in Carnot Groups and Geometry of Hörmander Vector Fields, PhD Thesis, Cardiff University, Cardiff (2018).Google Scholar
  14. E. Francini: Starshapedness of level sets for solutions of nonlinear elliptic equations, Math. Nachr 193 (1998) 49–56.https://doi.org/10.1002/mana.19981930106Google Scholar
  15. N. Garofalo, F. Tournier: New properties of convex functions in the Heisenberg group, Trans. Amer. Math. Soc. 358(5) (2006) 2011–2055 (electronic).https://doi.org/10.1090/S0002-9947-05-04016-XGoogle Scholar
  16. A. Greco, W. Reichel: Existence and starshapedness for the Lane-Emden equation, Applicable Analysis 78 (2001) 21–32.https://doi.org/10.1080/00036810108840923Google Scholar
  17. P. M. Gruber, T. I. Zamfirescu: Generic properties of compact starshapedsets, Proc. Amer. Math. Soc. 108(1) (1990) 207–214.https://doi.org/10.2307/2047715Google Scholar
  18. C. E. Gutiérrez, A. Montanari: On the second order derivatives of convex functions on the Heisenberg group, Ann. Sc. Norm. Super. Pisa Cl. Sci. (5), 3(2) (2004) 349–366.https://doi.org/10.2422/2036-2145.2004.2.03Google Scholar
  19. S. Jarohs, T. Kulczycki, P. Salani: Starshape of the superlevel sets of solutions to equations involving the fractional Laplacian in starshaped rings, Math. Nachrichten 292(5) (2019) 1008–1021.https://doi.org/10.1002/mana.201700226Google Scholar
  20. P. Juutinen, G. Lu, J. J. Manfredi, B. Stroffolini: Convex functions on Carnot groups, Rev. Mat. Iberoam. 23(1) (2007) 191–200.https://doi.org/10.4171/rmi/490Google Scholar
  21. G. Lu, J. J. Manfredi, B. Stroffolini: Convex functions in the Heisenberg group, Calc. Var. Partial Differential Equations 19(1) (2004) 1–22.https://doi.org/10.1007/s00526-003-0190-4Google Scholar
  22. V. Magnani: Lipschitz continuity, Aleksandrov theorem and characterizations for H-convex functions, Math. Ann. 334(1) (2006) 199–233.https://doi.org/10.1007/s00208-005-0717-4Google Scholar
  23. R. Montgomery: A Tour of Sub-Riemannian Geometries, their Geodesics and Application, Mathematical Surveys and Monographs 91, American Mathematical Society, Providence (2002).Google Scholar
  24. R. Monti, M. Rickly: Geodetically convex sets in the Heisenberg group, J. Convex Analysis 12(1) (2005) 187–196.https://doi.org/10.68381/jca12013Google Scholar
  25. M. Rickly: First order regularity of convex functions on Carnot groups, J. Geom. Anal. 16 (2006) 679–702.https://doi.org/10.1007/BF02922136Google Scholar
  26. E. E. Robkin: Characterizations of Starshaped Sets, University of California, Los Angeles (1965).Google Scholar
  27. P. Salani: Starshapedness of level sets of solutions to elliptic PDEs, Applicable Analysis 84(12) (2005) 1185–1197.https://doi.org/10.1080/00036810412331297262Google Scholar
  28. T. Shermer, G. Toussaint: Characterizations of star-shaped, L-convex and convex polygons, Int. J. Computer Inform. Engineering 7(1) (2013).Google Scholar
  29. F. A. Valentine: Convex Sets, McGraw-Hill, New York (1964).Google Scholar
  30. C. Wang: Viscosity convex functions on Carnot groups, Proc. Amer. Math. Soc. 133(4) (2005) 1247–1253.https://doi.org/10.1090/S0002-9939-04-07836-0Google Scholar

F. Dragoni, D. Filali. “Starshaped and Convex Sets in Carnot Groups and in the Geometries of Vector Fields.” Journal of Convex Analysis 26 (2019), No. 4, 1349–1372. https://doi.org/10.68381/jca26072