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Aleksandrov problem for isometric mappings

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Let X, Y be two metric spaces, with respective distances d_1, d _ { 2 } (cf. also Metric space). A mapping f : X \rightarrow Y is defined to be an isometry if d_{2} ( f ( x ) , f ( y ) ) = d _ { 1 } ( x , y ) for all x , y \in X. A mapping f : X \rightarrow Y is said to preserve the distance r if for all x , y \in X with d _ { 1 } ( x , y ) = r one has d _ { 2 } ( f ( x ) , f ( y ) ) = r. A.D. Aleksandrov has posed the problem whether the existence of a single preserved distance for some mapping f implies that f is an isometry (cf. [a1]).

Even if X, Y are normed vector spaces, the above problem is not easy to answer (note that, in this case, taking r = 1 is no loss of generality). For example, the following question has not been solved yet (as of 2000): Is a mapping f from \mathbf{R} ^ { 2 } to \mathbf{R} ^ { 3 } preserving unit distance necessarily an isometry (cf. [a17])?

The discussion of Aleksandrov's problem under certain additional conditions on the given mapping preserving unit distance has led to several interesting and new problems (cf. [a14], [a15], [a16], [a18], [a17]).

The Aleksandrov problem has been solved for Euclidean spaces X = Y = \mathbf{R} ^ { n }: For 2 \leq n < \infty, the answer is positive [a2], while for n = 1 , \infty, the answer is negative [a2], [a5], [a13]. In general normed vector spaces, the answer is positive for a mapping that is contractive, surjective and preserves the unit distance. The problem also has a positive solution when X and Y are strictly convex vector spaces, provided f is a homeomorphism and the dimension of X is greater than 2 (cf. [a12], [a20]).

The Aleksandrov problem has also been solved in some special cases of mappings f : X \rightarrow Y which preserve two distances with an integer ratio greater than 1, with X and Y strictly convex vector spaces and the dimension of X greater than 1 (cf. [a3], [a16], [a17]). Furthermore, when X, Y are Hilbert spaces and the dimension of X is greater than 1, a lot of work has been done (cf. [a21], [a22], [a23]; for example, when f preserves the two distances 1 and \sqrt { 3 }; when \operatorname{dim} X \geq 3 and f preserves 1 and \sqrt { 2 }, then f is an affine isometry, etc.).

Problems connected with stability of isometries as well as non-linear perturbations of isometries have been extensively studied in [a4], [a5], [a6], [a7], [a8], [a9], [a10], [a11].

References

[a1] A.D. Aleksandrov, "Mapping of families of sets" Soviet Math. Dokl. , 11 (1970) pp. 116–120
[a2] F.S. Beckman, D.A. Quarles, "On isometries of Euclidean spaces" Proc. Amer. Math. Soc. , 4 (1953) pp. 810–815
[a3] W. Benz, H. Berens, "A contribution to a theorem of Ulam–Mazur" Aquat. Math. , 34 (1987) pp. 61–63
[a4] D.G. Bourgain, "Approximate isometries" Bull. Amer. Math. Soc. , 52 (1946) pp. 704–714
[a5] K. Ciesielski, Th.M. Rassias, "On some properties of isometric mappings" Facta Univ. Ser. Math. Inform. , 7 (1992) pp. 107–115
[a6] G. Dolinar, "Generalized stability of isometries" J. Math. Anal. Appl. , 202 (2000) pp. 39–56
[a7] J. Gevirtz, "Stability of isometries on Banach spaces" Proc. Amer. Math. Soc. , 89 (1983) pp. 633–636
[a8] P.M. Gruber, "Stability of isometries" Trans. Amer. Math. Soc. , 245 (1978) pp. 263–277
[a9] J. Lindenstrauss, A. Szankowski, "Non linear perturbations of isometries" Astérisque , 131 (1985) pp. 357–371
[a10] D.H. Hyers, S.M. Mazur, "On approximate isometries" Bull. Amer. Math. Soc. , 51 (1945) pp. 288–292
[a11] S.M. Mastir, S. Ulam, "Sur les transformations isométriques d'espaces vectoriels normés" C.R. Acad. Sci. Paris , 194 (1932) pp. 946–948
[a12] B. Mielnik, Th.M. Rassias, "On the Aleksandrov problem of conservative distances" Proc. Amer. Math. Soc. , 116 (1992) pp. 1115–1118
[a13] Th.M. Rassias, "Some remarks on isometric mappings" Facta Univ. Ser. Math. Inform. , 2 (1987) pp. 49–52
[a14] Th.M. Rassias, "Is a distance one preserving maping between metric space always an isometry?" Amer. Math. Monthly , 90 (1983) pp. 200
[a15] Th.M. Rassias, "The stability of linear mappings and some problems on isometries" , Proc. Internat. Conf. Math. Anal. Appl. Kuwait, 1985 , Pergamon (1988) pp. 175–184
[a16] Th.M. Rassias, "Mappings that preserve unit distance" Indian J. Math. , 32 (1990) pp. 275–278
[a17] Th.M. Rassias, "Properties of isometries and approximate isometries" , Recent Progress in Inequalities , Kluwer Acad. Publ. (1998) pp. 325–345
[a18] Th.M. Rassias, "Remarks and problems" Aequat. Math. , 39 (1990) pp. 304
[a19] Th.M. Rassias, "Remarks and problems" Aequat. Math. , 56 (1998) pp. 304–306
[a20] Th.M. Rassias, P. Semrl, "On the Masur–Ulam theorem and the Aleksandrov probiem for unit distance preserving mapping" Proc. Amer. Math. Soc. , 118 (1993) pp. 919–925
[a21] Th.M. Rassias, Shuhuang Xiang, "On mappings with conservative distance and the Mazur–Ulam theorem" Publ. EPT. , to appear (2000)
[a22] Shuhuang Xiang, "Aleksandrov problem and mappings which preserves distances" , Funct. Equations and Inequalities , Kluwer Acad. Publ. (2000) pp. 297–323
[a23] Shuhuang Xiang, "Mappings of conservative distances and the Mazur–Ulam theorem" J. Math. Anal. Appl. , 254 (2001) pp. 262–274
How to Cite This Entry:
Aleksandrov problem for isometric mappings. Encyclopedia of Mathematics. URL: http://encyclopediaofmath.org/index.php?title=Aleksandrov_problem_for_isometric_mappings&oldid=50017
This article was adapted from an original article by Shuhuang Xiang (originator), which appeared in Encyclopedia of Mathematics - ISBN 1402006098. See original article