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polydisc (Definition)
Definition 1   We denote the set
$\displaystyle D^n(z,r) := \{ w \in {\mathbb{C}}^n \mid \lvert z_k - w_k \rvert < r$    for all $\displaystyle k = 1,\ldots,n \}$    

an open polydisc. We can also have polydiscs of the form
$\displaystyle D^1(z_1,r_1) \times \ldots \times D^1(z_n,r_n) .$    

The set $ \partial D^1(z_1,r_1) \times \ldots \times \partial D^1(z_n,r_n)$ is called the distinguished boundary of the poydisc.

Be careful not to confuse this with the open ball in $ {\mathbb{C}}^n$ as that is defined as

$\displaystyle B(z,r) := \{ w \in {\mathbb{C}}^n \mid \lvert z - w \rvert < r \} .$    

When $ n > 1$ then open balls and open polydiscs are not biholomorphically equivalent (there is no 1-1 biholomorphic mapping between the two).

It is common to write $ \bar{D}^n(z,r)$ for the closure of the polydisc. Be careful with this notation however as some texts outside of complex analysis use $ D(x,r)$ and the term “disc” to represent a closed ball in two real dimensions.

Also note that when $ n=2$ the term bidisc is sometimes used.

Bibliography

1
Lars Hörmander. An Introduction to Complex Analysis in Several Variables, North-Holland Publishing Company, New York, New York, 1973.
2
Steven G. Krantz. Function Theory of Several Complex Variables, AMS Chelsea Publishing, Providence, Rhode Island, 1992.



"polydisc" is owned by jirka.
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Other names:  open polydisc
Also defines:  bidisc, distinguished boundary
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Cross-references: dimensions, real, represent, complex analysis, closure, biholomorphic mapping, biholomorphically equivalent, open ball
There are 7 references to this entry.

This is version 5 of polydisc, born on 2004-07-26, modified 2005-11-03.
Object id is 6030, canonical name is Polydisc.
Accessed 3719 times total.

Classification:
AMS MSC32-00 (Several complex variables and analytic spaces :: General reference works )
 32A07 (Several complex variables and analytic spaces :: Holomorphic functions of several complex variables :: Special domains )

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