\begin{definition}[Definition:Multiindex/Modulus]
Let $k = \sequence {k_j}_{j \mathop \in J}$ be a multiindex.
The '''modulus''' of such a multiindex $k$  is defined by:
:$\ds \size k = \sum_{j \mathop \in J} k_j$
Note that, since by definition all but finitely many of the $k_j$ are zero, this summation is convergent.
Category:Definitions/Polynomial Theory
\end{definition}