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Integration of polyharmonic functions. (English) Zbl 0860.31003
The main purpose of the paper is to extend two well-known quadrature formulas, which are precise for all algebraic polynomials of degree $$2m-1$$, to the corresponding multivariate analogues, which are exact for the $$m$$-harmonic functions. Observing the analogy between some well-known theorems concerning integration of polyharmonic functions and results about quadrature formulas, the author searches the possibility of extending some Green’s formulas as, for instance $$\int_B u(x)dx= (1/n) \int_S u(x)d\sigma$$, for harmonic functions in order to increase the polyharmonic order of precision (a notion introduced in the paper).
The main result of the paper concerns explicit representations and sharp error bounds for such extensions. The principal tool in the proofs is an extension of the notion of univariate monosplines introduced by Schoenberg. The second chapter of the paper is devoted to this problem.

##### MSC:
 31B30 Biharmonic and polyharmonic equations and functions in higher dimensions 65D32 Numerical quadrature and cubature formulas 65D07 Numerical computation using splines 35J30 Higher-order elliptic equations
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##### References:
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