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arXiv 1906.06124math.NAcs.NA
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四个美丽的quadrature规则

Four beautiful quadrature rules

Mário M. Graça

摘要:

给出了一个从一对伴随规则及其关联规则计算积分$I(f)=\displaystyle \int_a^b f(x) dx$的近似的框架。我们表明,一个关联规则是两个同伴规则的加权平均。特别地,梯形(T)和辛普森(S)规则分别是同伴对(L,R)和(T,M)的加权平均,其中L是左矩形,R是右矩形,M是中点规则。由于L、R、T和M完全再现了数字$π=\displaystyle \int_0^π2\, \sin^2(x) dx$,我们将它们命名为四个“{美丽}”规则。在这个例子中,规则的几何解释表明超越数$π$在建筑设计中的可能应用,证明了上述规则的美丽属性。作为补充,我们考虑其他适当的被积函数$f$,应用复合规则,以获得良好的近似$π$,如工作的数值例子。

英文摘要:

A framework is presented to compute approximations of an integral $I(f)=\displaystyle \int_a^b f(x) dx$ from a pair of companion rules and its associate rule. We show that an associate rule is a weighted mean of two companion rules. In particular, the trapezoidal (T) and Simpson (S) rules are weighted means of the companion pairs (L,R) and (T,M) respectively, with L the left rectangle, R the right rectangle and M the midpoint rules. As L,R,T and M reproduce exactly the number $π=\displaystyle \int_0^π2\, \sin^2(x) dx$, we named them the four "{beautiful}" \ rules. For this example the geometrical interpretation of the rules suggest possible applications of the transcendental number $π$ in architectural design, justifying the attribute beautiful given to the mentioned rules. As a complement we consider other appropriate integrand functions $f$, applying composite rules in order to obtain good approximations of $π$, as shown in the worked numerical examples.

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