Geodesic
Expansion over a system of shifts of pyramidal functions with a square base
Vestnik Moskovskogo universiteta. Matematika, mehanika, no. 3 (2014), pp. 3-7 
S. M. Lytkin. Expansion over a system of shifts of pyramidal functions with a square base. Vestnik Moskovskogo universiteta. Matematika, mehanika, no. 3 (2014), pp. 3-7. http://geodesic.mathdoc.fr/item/VMUMM_2014_3_a0/
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     title = {Expansion over a system of shifts of pyramidal functions with a square base},
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     url = {http://geodesic.mathdoc.fr/item/VMUMM_2014_3_a0/}
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Voir la notice de l'article provenant de la source Math-Net.Ru

A method for approximation of functions of two variables by a linear combination of nonnegative piecewise linear functions with a compact support is presented. Two quadratic pyramids are used as generating functions for the system of shifts. The accuracy of this local method is proved to have the same order as the best approximation by piecewise linear functions.

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