Abstract
We show that integrating a polynomial f of degree t on an arbitrary simplex (with respect to Lebesgue measure) reduces to evaluating t homogeneous related Bombieri polynomials of degree \(j=1,2,\ldots ,t\), each at a unique point \(\varvec{\xi }_j\) of the simplex. This new and very simple formula could be exploited in finite (and extended finite) element methods, as well as in applications where such integrals must be evaluated. A similar result also holds for a certain class of positively homogeneous functions that are integrable on the canonical simplex.
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Notes
\(f_j\) is the unique form of degree j which is the sum of all monomials of degree j of f (with their coefficient).
A real-valued function \(f:({\mathbb {R}}\setminus \{0\})^n\rightarrow {\mathbb {R}}\) is completely monotone if \((-1)^k\frac{\partial ^k f}{\partial x_{i_1}\cdots \partial x_{i_k}}({\mathbf {x}})\ge 0\) for all \({\mathbf {x}}\in ({\mathbb {R}}\setminus \{0\})^n\) and for all index sequences \(1\le i_1\le \cdots \le i_k\le n\) of arbitrary length k.
In number theory, the Waring problem consists of writing any positive integer as a sum of a fixed number g(n) of nth powers of integers, where g(n) depends only on n. It generalizes to forms as a generic form of degree d can be written as a sum of s d-powers of linear forms; s is called the Waring rank of the form.
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Communicated by Elisabeth Larsson.
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Research funded by the European Research Council (ERC) under the European’s Union Horizon 2020 research and innovation program (Grant Agreement 666981 TAMING).
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Lasserre, J.B. Simple formula for integration of polynomials on a simplex. Bit Numer Math 61, 523–533 (2021). https://doi.org/10.1007/s10543-020-00828-x
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DOI: https://doi.org/10.1007/s10543-020-00828-x