
doi: 10.1007/bf02384491
The local three squares problem concerns the question whether functions defined on a cube in \(\mathbb{R}^d\) are determined from their averages on certain smaller cubes. The authors prove a quite general result, namely: fix the dimension \(d\), consider positive numbers \(r_1, \dots, r_{d+1}\), and take any \(R\geq \sum_{i=1}^{d+1}r_i\). Then any function \(f\in L^2([-R,R]^d)\) is determined by its averages over cubes of side \(r_i\) that are completely contained in \([-R,R]^d\) and have edges parallel to the coordinate axes, if and only if \(r_i/r_j\) is irrational for \(i\neq j\). The main technical tool is the sampling theory for bandlimited functions.
1010 Mathematics, Trigonometric moment problems in one variable harmonic analysis, Pompeiu problems, 1010 Mathematik, exact sequences, Switching theory, application of Boolean algebra; Boolean functions, irregular sampling, Completeness of sets of functions in one variable harmonic analysis, Nontrigonometric harmonic analysis involving wavelets and other special systems, three squares theorem, nonperiodic sampling
1010 Mathematics, Trigonometric moment problems in one variable harmonic analysis, Pompeiu problems, 1010 Mathematik, exact sequences, Switching theory, application of Boolean algebra; Boolean functions, irregular sampling, Completeness of sets of functions in one variable harmonic analysis, Nontrigonometric harmonic analysis involving wavelets and other special systems, three squares theorem, nonperiodic sampling
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