@Article{ATA-34-336,
author = {Ricardo Estrada},
title = {Harmonic Polynomials via Differentiation},
journal = {Analysis in Theory and Applications},
year = {2018},
volume = {34},
number = {4},
pages = {336--347},
abstract = {<p style="text-align: justify;">It is well-known that if $p$ is a homogeneous polynomial of degree $k$ in $n$ variables, $p∈\mathcal{P}_k$, then the ordinary derivative $p(∇) (r^{2−n})$ has the form $A_{n,k}\Upsilon(x)r^{2−n−2k}$ where $A_{n,k}$ is a constant and where $\Upsilon$ is a harmonic homogeneous polynomial of degree $k,$ $\Upsilon\in \mathcal{H}_k$, actually the projection of $p$ onto $\mathcal{H}_k$. Here we study the distributional
derivative $p(\overline{∇})(r^{2−n})$ and show that the ordinary part is still a multiple of $\Upsilon$, but that
the delta part is independent of $\Upsilon$, that is, it depends only on $p−\Upsilon$. We also show that
the exponent $2−n$ is special in the sense that the corresponding results for $p(∇)(r^α)$ do not hold if $α\neq 2−n$.<br/>Furthermore, we establish that harmonic polynomials appear as multiples of $r^{2−n−2k−2k&#39;}$&nbsp;when $p(∇)$ is applied to harmonic multipoles of the form $\Upsilon&#39;(x)r^{2−n−2k&#39;}$ for some $\Upsilon&#39; \in \mathcal{H}_k$.</p>},
issn = {1573-8175},
doi = {https://doi.org/10.4208/ata.OA-2017-0062},
url = {http://global-sci.org/intro/article_detail/ata/12847.html}
}