**Abstract:**
We investigate numerical differentiation formulas on irregular centers in two or
more variables that are exact for polynomials of a given order and minimize an
absolute seminorm of the weight vector. Error bounds are given in terms of a
growth function that carries the information about the geometry of the centers.
Specific forms of weighted l1 and weighted least squares minimization are proposed
that produce numerical differentiation formulas with particularly good performance
in numerical experiments. The results are of interest in particular for
meshless generalized finite difference methods as they provide a consistency
error analysis for such methods.

**Preprint version:**
pdf
arXiv:1611.05001

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