We consider a countable quasilinear system of differential equations defined on an infinite-dimensional torus. The problem is to find sufficient conditions under which the investigated system of equations possesses an invariant torus in the space of bounded numerical sequences whose generating function can be approximated with any given accuracy by a generating function of the invariant torus for some countable linear system defined on a finite-dimensional torus. This enables us to approximate (with any given degree of accuracy) a one-parameter family of solutions almost periodic in Bohr’s sense of a given system of equations by a family of quasiperiodic solutions of the above-mentioned linear system uniformly in the parameter.
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Translated from Neliniini Kolyvannya, Vol. 23, No. 4, pp. 553–564, October–December, 2020.
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Teplinsky, Y.V. On the Invariant Tori of Quasilinear Countable Systems of Differential Equations Defined on Infinite–Dimensional Tori. J Math Sci 263, 327–340 (2022). https://doi.org/10.1007/s10958-022-05928-3
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DOI: https://doi.org/10.1007/s10958-022-05928-3