# Wydawnictwa / Banach Center Publications / Wszystkie tomy

## Ideal interpolation: Mourrain's condition vs. $D$-invariance

### Tom 72 / 2006

Banach Center Publications 72 (2006), 49-55 MSC: Primary 41A05, 41A10, 41A63; Secondary 13P10. DOI: 10.4064/bc72-0-3

#### Streszczenie

Mourrain \cite{Mo} characterizes those linear projectors on a finite-dimensional polynomial space that can be extended to an ideal projector, i.e., a projector on polynomials whose kernel is an ideal. This is important in the construction of normal form algorithms for a polynomial ideal. Mourrain's characterization requires the polynomial space to be connected to 1', a condition that is implied by $D$-invariance in case the polynomial space is spanned by monomials. We give examples to show that, for more general polynomial spaces, $D$-invariance and being connected at 1' are unrelated, and that Mourrain's characterization need not hold when his condition is replaced by $D$-invariance.

#### Autorzy

• C. de BoorPOB 1076, Eastsound, WA 98245, U.S.A.
e-mail

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