Combining methods from analysis and (convex) geometry, we derive geometric properties of generalizations of the following four classical types of bifocal curves: ellipses, hyperbolas, Cassini curves, and Apollonius circles. It is natural to consider them together, since the points of one such curve have (in the same sequence) constant sum, constant difference, constant product, and constant ratio of distances to the two given foci. Our generalization of this classical concept is two-fold: first we extend the used distance functions from the Euclidean and the (in the literature only partially investigated) normed case to gauges, where the unit ball no longer has to be symmetric with respect to the origin. And second we study, in the cases where it makes sense (ellipses and Cassini curves), even multifocal curves. Most of our investigations are even extended to higher dimensions. We also survey known results about these classes of curves which are close to our purpose (namely, referring to the normed case, to multifocality, and to higher dimensions), since no comparable survey exists and these results are widespread and not systematized in the literature.

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  1. G. Arcos, G. Montilla, J. Ortega, M. Paluszny: Shape control of 3D lemniscates, Math. Comput. Simul. 73(1–4) (2006) 21–27.https://doi.org/10.1016/j.matcom.2006.06.001Google Scholar
  2. A. F. Beardon: The Apollonian metric of a domain in Rn, in: Quasiconformal Mappings and Analysis (Ann Arbor, 1995), P. Duren et al. (ed.), Springer, New York (1998) 91–108.https://doi.org/10.1007/978-1-4612-0605-7_8Google Scholar
  3. M. Berger: Geometry II, Springer, Berlin (1987).Google Scholar
  4. V. Boltyanski, H. Martini, V. Soltan: Geometric Methods and Optimization Problems, Kluwer, Dordrecht (1999).https://doi.org/10.1007/978-1-4615-5319-9Google Scholar
  5. O. Bottema: The isodynamic points of a tetrahedron, Nieuw Arch. Wiskd., III. Ser 7 (1959) 91–94.Google Scholar
  6. A. Brauer: Limits for the characteristic roots of a matrix. II, Duke Math. J. 14 (1947) 21–26.https://doi.org/10.1215/S0012-7094-47-01403-8Google Scholar
  7. A. Brauer: Limits for the characteristic roots of a matrix. IV. Applications to stochastic matrices, Duke Math. J. 19 (1952) 75–91.https://doi.org/10.1215/S0012-7094-52-01910-8Google Scholar
  8. E. Brieskorn, H. Knörrer: Plane Algebraic Curves, Birkhäuser, Basel (1986).https://doi.org/10.1007/978-3-0348-5097-1Google Scholar
  9. J. Cassini: Éleménts d’astronomie, Imprimerie royale, Paris (1740).Google Scholar
  10. L. P. Chew, R. L. S. Drysdale: Voronoi diagrams based on convex distance functions, in: Proc. Sympos. Computational Geometry (Baltimore, 1985), J. O’Rourke (ed.), ACM, New York (1985) 235–244.https://doi.org/10.1145/323233.323264Google Scholar
  11. F. Chiochiu: Holomorphic functions in domains bounded by Cassini curves, An. Univ. Bucures, ti Mat.-Mec. 20(2) (1971) 47–61.Google Scholar
  12. H. S. M. Coxeter: Introduction to Geometry, John Wiley & Sons, New York (1961).Google Scholar
  13. H. H. Cuenya, F. E. Levis: A property of the planar measure of the lemniscates, J. Math. Anal. Appl. 336(2) (2007) 953–961.https://doi.org/10.1016/j.jmaa.2007.03.034Google Scholar
  14. I. A. Danelič: Normed spaces which satisfy Apollonius’ theorem, Mat. Zametki 20(2) (1976) 247–252 (in Russian); Math. Notes 20(2) (1976) 696–699 (in English).https://doi.org/10.1007/BF01155877Google Scholar
  15. A. Di Biasio, C. Cametti: Effect of the shape of human erythrocytes on the evaluation of the passive electrical properties of the cell membrane, Bioelectrochemistry 65(2) (2005) 163–169.https://doi.org/10.1016/j.bioelechem.2004.09.001Google Scholar
  16. K. Driver, M. Möller: Zeros of the hypergeometric polynomials F (−n, b; −2n; z), J. Approx. Theory 110(1) (2001) 74–87.https://doi.org/10.1006/jath.2000.3548Google Scholar
  17. E. Ehrhart: Über eine Klasse von Eilinien und Eiflaechen, Sitzungsber. Österr. Akad. Wiss., Math.-Naturwiss. Kl., Abt. II 190(8–10) (1982) 495–513.Google Scholar
  18. P. Erdős, J. S. Hwang: On a geometric property of lemniscates, Aequationes Math. 17(2–3) (1978) 344–347.https://doi.org/10.1007/BF01818573Google Scholar
  19. P. Erdős, I. Vincze: On the approximation of convex, closed plane curves by multifocal ellipses, J. Appl. Probab. 19A (1982) 89–96.https://doi.org/10.1017/S0021900200034483Google Scholar
  20. A. Fankhänel: On conics in Minkowski planes, Extr. Math. 27(1) (2012) 13–29.Google Scholar
  21. K. Fladt: Analytische Geometrie spezieller ebener Kurven, Akademische Verlagsgesellschaft, Frankfurt am Main (1962).Google Scholar
  22. C. J. Friedrich: Alfred Weber’s Theory of the Location of Industries, University of Chicago Press, Chicago (1929).Google Scholar
  23. F. Gomes Teixeira: Traité des Courbes Spéciales Remarquables Planes et Gauches. Tomes I, II, III, Jacques Gabay, Paris (1995).Google Scholar
  24. W. H. Greub: A parametric representation of the sphere with p handles, C. R. Math. Acad. Sci., Soc. R. Can. 5(3) (1983) 143–148.Google Scholar
  25. C. Groß, T.-K. Strempel: Topologie verallgemeinerter Kegelschnitte, Math. Semesterber. 44(2) (1997) 139–151.https://doi.org/10.1007/s005910050030Google Scholar
  26. C. Groß, T.-K. Strempel: On generalizations of conics and on a generalization of the Fermat–Torricelli problem, Amer. Math. Monthly 105(8) (1998) 732–743.https://doi.org/10.1080/00029890.1998.12004955Google Scholar
  27. P. Hartman, F. A. Valentine: On generalized ellipses, Duke Math. J. 26 (1959) 373–385.https://doi.org/10.1215/S0012-7094-59-02635-3Google Scholar
  28. J. Hellmers, E. Eremina, T. Wriedt: Simulation of light scattering by biconcave Cassini ovals using the nullfield method with discrete sources, J. Opt. A: Pure Appl. Opt. 8(1) (2006) 1–9.https://doi.org/10.1088/1464-4258/8/1/001Google Scholar
  29. G. Herzog, C. Schmoeger: The Brauer–Ostrowski theorem for matrices of operators, Integral Equations Oper. Theory 57(4) (2007) 513–520.https://doi.org/10.1007/s00020-006-1472-yGoogle Scholar
  30. D. Hilbert, S. Cohn-Vossen: Anschauliche Geometrie, Springer, Berlin (1932) (in German); Geometry and the Imagination, Chelsea, New York (1952) (in English).https://doi.org/10.1007/978-3-662-36685-1Google Scholar
  31. Á. G. Horváth, H. Martini: Conics in normed planes, Extr. Math. 26(1) (2011) 29–43.Google Scholar
  32. J. A. Hoskins, W. D. Hoskins, R. G. Stanton: A generalization of the circumcircle theorem, J. Geom. 38(1–2) (1990) 52–58.https://doi.org/10.1007/BF01222895Google Scholar
  33. T. Jahn, Y. S. Kupitz, H. Martini, C. Richter: Minsum location extended to gauges and to convex sets, J. Optim. Theory Appl. 166(3) (2015) 711–746.https://doi.org/10.1007/s10957-014-0692-6Google Scholar
  34. M. Karataş: A multi foci closed curve: Cassini oval, its properties and applications, Doğuş Univ. J. 14(2) (2013) 231–248.https://doi.org/10.31671/dogus.2018.108Google Scholar
  35. D. Kirby, F. Rhodes: Pencils of circles of equal potentials, J. Geom. 50(1–2) (1994) 118–123.https://doi.org/10.1007/BF01222669Google Scholar
  36. R. Klén, M. Vuorinen: Apollonian circles and hyperbolic geometry, J. Anal. 19 (2011) 41–60.Google Scholar
  37. O. N. Kosukhin: On the rate of approximation of closed Jordan curves by lemniscates, Mat. Zametki 77(6) (2005) 861–876 (in Russian); Math. Notes 77(5–6) (2005) 794–808 (in English).https://doi.org/10.4213/mzm2543https://doi.org/10.1007/s11006-005-0080-5Google Scholar
  38. D. K. Kulshrestha, T. W. Sag: Symmetric k-ellipses with limiting eccentricity, Geom. Dedicata 30(2) (1989) 183–195.https://doi.org/10.1007/BF00181550Google Scholar
  39. J. D. Lawrence: A Catalog of Special Plane Curves, Dover, New York (1972).Google Scholar
  40. M. Lentini, M. Paluszny: On grid generation with lemniscates of two and three foci, Comput. Appl. Math. 32(3) (2013) 495–507.https://doi.org/10.1007/s40314-013-0032-8Google Scholar
  41. G. Loria: Spezielle algebraische und transcendente ebene Kurven. Theorie und Geschichte, Teubner, Leipzig (1902).Google Scholar
  42. L. Ma: Bisectors and Voronoi Diagrams for Convex Distance Functions, PhD Thesis, Fernuniversität Hagen (2000).Google Scholar
  43. W. Makuchowski: Circles of Apollonius, Zesz. Nauk. Wyższ. Szk. Pedagog. Opolu, Mat. 25 (1987) 5–17 (in Polish).Google Scholar
  44. A. I. Markushevich: Theory of Functions of a Complex Variable. Vol. I, Prentice-Hall, Englewood Cliffs (1965).Google Scholar
  45. H. Martini, U. Schiel: Cassini-Kurven in der Lichtfeldtheorie, J. Geom. 45(1–2) (1992) 121–130.https://doi.org/10.1007/BF01225771Google Scholar
  46. H. Martini, K. Swanepoel: The geometry of Minkowski spaces – a survey, Part II, Expo. Math. 22(2) (2004) 93–144.https://doi.org/10.1016/S0723-0869(04)80009-4Google Scholar
  47. H. Martini, K. Swanepoel, G. Weiß: The geometry of Minkowski spaces – a survey, Part I, Expo. Math. 19(2) (2001) 97–142.https://doi.org/10.1016/S0723-0869(01)80025-6Google Scholar
  48. H. Martini, S. Wu: Cassini curves in normed planes, Results Math. 63(3-4) (2013) 1159–1175.https://doi.org/10.1007/s00025-012-0260-zGoogle Scholar
  49. H. Martini, S. Wu: Classical curve theory in normed planes, Comput. Aided Geom. Design 31(7–8) (2014) 373–397.https://doi.org/10.1016/j.cagd.2014.03.003Google Scholar
  50. A. Melman: Ovals of Cassini for Toeplitz matrices, Linear Multilinear Algebra 60(2) (2012) 189–199.https://doi.org/10.1080/03081087.2011.580280Google Scholar
  51. A. Melman: A single oval of Cassini for the zeros of a polynomial, Linear Multilinear Algebra 61(2) (2013) 183–195.https://doi.org/10.1080/03081087.2012.670637Google Scholar
  52. Z. A. Melzak, J. S. Forsyth: Polyconics. I. Polyellipses and optimization, Quart. Appl. Math. 35(2) (1977/78) 239–255.https://doi.org/10.1090/qam/448883Google Scholar
  53. L. J. Mordell: On a distance-function inequality and A. Brauer’s inequality for Cassini curves, J. Anal. Math. 6 (1958) 177–181.https://doi.org/10.1007/BF02790235Google Scholar
  54. B. Nagy, V. Totik: Sharpening of Hilbert’s lemniscate theorem, J. Anal. Math. 96 (2005) 191–223.https://doi.org/10.1007/BF02787828Google Scholar
  55. J. A. Nickel: Bipolar harmonics on a circular drum, Math. Modelling 1(4) (1980) 369–374.https://doi.org/10.1016/0270-0255(80)90046-9Google Scholar
  56. J. A. Nickel: A budget of inversions, Math. Comput. Modelling 21(6) (1995) 87–93.https://doi.org/10.1016/0895-7177(95)00025-WGoogle Scholar
  57. S. Nickel, J. Puerto: Location Theory – A Unified Approach, Springer, Berlin (2005).Google Scholar
  58. J. Nie, P. A. Parrilo, B. Sturmfels: Semidefinite representation of the k-ellipse, in: Algorithms in Algebraic Geometry (Minneapolis, 2006), A. Dickenstein et al. (ed.), Springer, New York (2008) 117–132.https://doi.org/10.1007/978-0-387-75155-9_7Google Scholar
  59. J. Nie, B. Sturmfels: Matrix cubes parameterized by eigenvalues, SIAM J. Matrix Anal. Appl. 31(2) (2009) 755–766.https://doi.org/10.1137/080722606Google Scholar
  60. A. M. Ostrowski: Note on a theorem by A. Brauer, Duke Math. J. 22 (1955) 469–470.https://doi.org/10.1215/S0012-7094-55-02252-3Google Scholar
  61. M. Paluszny, G. Montilla, J. R. Ortega: Lemniscates 3D: a CAGD primitive?, Numer. Algorithms 39(1–3) (2005) 317–327.https://doi.org/10.1007/s11075-004-3645-6Google Scholar
  62. G. Peano: Applicazioni Geometriche del Calcolo Infinitesimale, Bocca, Torino (1887).https://doi.org/10.3792/chmm/1424377228Google Scholar
  63. D. Pedoe: Geometry. A Comprehensive Course, 2nd Ed., Dover, New York (1988).Google Scholar
  64. W. M. Pieper: Multifocal surfaces and algorithms for displaying them, J. Geom. Graph. 10(1) (2006) 37–62.Google Scholar
  65. M. Ponce, P. Santibáñez: On equidistant sets and generalized conics: the old and the new, Amer. Math. Monthly 121(1) (2014) 18–32.https://doi.org/10.4169/amer.math.monthly.121.01.018Google Scholar
  66. T. A. Rakcheeva: Multifocus lemniscates: approximation of curves, Zh. Vychisl. Mat. Mat. Fiz. 50(11) (2010) 2060–2072.https://doi.org/10.1134/S0965542510110187Google Scholar
  67. T. A. Rakcheeva: Focal approximation on the complex plane, Zh. Vychisl. Mat. Mat. Fiz. 51(11) (2011) 1963–1972.https://doi.org/10.1134/S0965542511110145Google Scholar
  68. L. Reichel: Newton interpolation at Leja points, BIT 30(2) (1990) 332–346.https://doi.org/10.1007/BF02017352Google Scholar
  69. R. T. Rockafellar: Convex Analysis, Princeton University Press, Princeton (1970).https://doi.org/10.1515/9781400873173Google Scholar
  70. G. Salmon: Analytische Geometrie der höheren ebenen Kurven, Teubner, Leipzig (1882).Google Scholar
  71. G. Scheffers: Funktionen über Abstände von festen Punkten, Württemberger Mitteilungen 2(2) (1900) 33–49.Google Scholar
  72. R. Schneider: Convex Bodies: The Brunn–Minkowski Theory, Cambridge University Press, Cambridge (1993).https://doi.org/10.1017/CBO9780511526282Google Scholar
  73. J. Sekino: n-ellipses and the minimum distance sum problem, Amer. Math. Monthly 106(3) (1999) 193–202.https://doi.org/10.1080/00029890.1999.12005030Google Scholar
  74. D. B. Shaffer: Distortion theorems for lemniscates and level loci of Green’s functions, J. Anal. Math. 17 (1966) 59–70.https://doi.org/10.1007/BF02788652Google Scholar
  75. D. B. Shaffer: On the convexity of lemniscates, Proc. Amer. Math. Soc. 26 (1970) 619–620.https://doi.org/10.1090/S0002-9939-1970-0271313-2Google Scholar
  76. D. B. Shaffer: Lemniscates and equipotentials, J. Approx. Theory 6 (1972) 431–438.https://doi.org/10.1016/0021-9045(72)90050-0Google Scholar
  77. C. K. Shene: On the circles of Apollonius associated with a triangle, J. Geom. 44(1–2) (1992) 171–176.https://doi.org/10.1007/BF01228291Google Scholar
  78. E. V. Shikin: Handbook and Atlas of Curves, CRC Press, Boca Raton (1995).Google Scholar
  79. E. N. Shonoda: Classification of conics and Cassini curves in Minkowski space-time plane, J. Egypt. Math. Soc., to appear.Google Scholar
  80. A. Y. Solynin, A. S. Williams: Area and the inradius of lemniscates, J. Math. Anal. Appl. 354(2) (2009) 507–517.https://doi.org/10.1016/j.jmaa.2009.01.012Google Scholar
  81. B. Sturmfels: Personal website at U.C. Berkeley, https://math.berkeley.edu/bernd/ (accessed April 7, 2015).Google Scholar
  82. Gy. Sz.-Nagy: Über die allgemeinen Lemniskaten, Acta Univ. Szeged. Sect. Sci. Math. 11 (1948) 207–224.Google Scholar
  83. Gy. Sz.-Nagy: Über die Lemniskatenflächen, Ann. Sc. Norm. Super. Pisa, Sci. Fis. Mat., III. Ser. 2 (1948) 39–53.Google Scholar
  84. Gy. Sz.-Nagy: Apollonische Kurven, Publ. Math. Debrecen 1 (1949) 73–88.https://doi.org/10.5486/PMD.1950.1.2-4.03Google Scholar
  85. Gy. Sz.-Nagy: Merkwürdige Punktgruppen bei allgemeinen Lemniskaten, Acta Univ. Szeged., Acta Sci. Math. 13 (1949) 1–13.Google Scholar
  86. Gy. Sz.-Nagy: Tschirnhaus’sche Eiflächen und Eikurven, Acta Math. Acad. Sci. Hung. 1 (1950) 36–45.https://doi.org/10.1007/BF02022550Google Scholar
  87. Gy. Sz.-Nagy: Tschirnhaus’sche Flächen und Kurven, Acta Math. Acad. Sci. Hung. 1 (1950) 167–181.https://doi.org/10.1007/BF02021309Google Scholar
  88. A. C. Thompson: Minkowski Geometry, Cambridge University Press, Cambridge (1996).https://doi.org/10.1017/CBO9781107325845Google Scholar
  89. E. W. von Tschirnhaus: Medicina mentis sive artis inveniendi praecepta generalia. Editio nova (1965), Transl. by J. Haussleitner, Johann Ambrosius Barth Verlag, Leipzig (1963) (in German).Google Scholar
  90. A. Varga, Cs. Vincze: On a lower and upper bound for the curvature of ellipses with more than two foci, Expo. Math. 26(1) (2008) 55–77.https://doi.org/10.1016/j.exmath.2007.06.003Google Scholar
  91. R. S. Varga: Gerschgorin disks, Brauer ovals of Cassini (a vindication) and Brualdi sets, Information 4(2) (2001) 171–178.Google Scholar
  92. R. S. Varga: Geršgorin and his Circles, Springer, Berlin (2004).https://doi.org/10.1007/978-3-642-17798-9Google Scholar
  93. Cs. Vincze, Á. Nagy: An introduction to the theory of generalized conics and their applications, J. Geom. Phys. 61(4) (2011) 815–828.https://doi.org/10.1016/j.geomphys.2010.12.003Google Scholar
  94. Cs. Vincze, Á. Nagy: On the theory of generalized conics with applications in geometric tomography, J. Approx. Theory 164(3) (2012) 371–390.https://doi.org/10.1016/j.jat.2011.11.004Google Scholar
  95. J. L. Walsh: Lemniscates and equipotential curves of Green’s function, Amer. Math. Monthly 42(1) (1935) 1–17.https://doi.org/10.1080/00029890.1935.11987668Google Scholar
  96. J. L. Walsh: On the convexity of the ovals of lemniscates, in: Studies in Mathematical Analysis and Related Topics, G. Szegő et al. (ed.), Stanford Univ. Press, Stanford (1962) 419–423.Google Scholar
  97. J. L. Walsh: Interpolation and Approximation by Rational Functions in the Complex Domain, 4th Ed., American Mathematical Society, Providence (1965).Google Scholar
  98. E. W. Weisstein: Apollonius pursuit problem, http://mathworld.wolfram.com/ApolloniusPursuitProblem.html (accessed April 7, 2015).Google Scholar
  99. H. Wieleitner: Spezielle ebene Kurven, Göschen, Leipzig (1908).Google Scholar
  100. A. C. Woods: A characterization of ellipsoids, Duke Math. J. 36 (1969) 1–6.https://doi.org/10.1215/S0012-7094-69-03601-1Google Scholar
  101. E. Yánez: Deformable orthogonal grids: lemniscates, J. Comput. Appl. Math. 104(1) (1999) 41–48.https://doi.org/10.1016/S0377-0427(98)00248-9Google Scholar
  102. V. A. Zalgaller, O. M. Merkulova: An analogue of the Appollonian circle on the Lobachevski plane and on the sphere, Zap. Nauchn. Semin. POMI 252 (1998) 21–32 (in Russian); J. Math. Sci., New York 104(4) (2001) 1264–1271 (in English).https://doi.org/10.1023/A:1011321612298Google Scholar
  103. T. Zamfirescu: Ellipsoïdes et hyperboloïdes généralisés, Atti Accad. Sci. Torino, Cl. Sci. Fis. Mat. Nat. 118(5–6) (1984) 314–324.Google Scholar
  104. X. Zhang, D. H Gu: A note on A. Brauer’s theorem, Linear Algebra Appl. 196 (1994) 163–174.https://doi.org/10.1016/0024-3795(94)90321-2Google Scholar

T. Jahn, H. Martini, C. Richter. “Bi- and Multifocal Curves and Surfaces for Gauges.” Journal of Convex Analysis 23 (2016), No. 3, 733–774. https://doi.org/10.68381/jca23029