Arun Ram
Department of Mathematics and Statistics
University of Melbourne
Parkville, VIC 3010 Australia
aram@unimelb.edu.au
Last update: 15 November 2012
Standard tableaux for type C in terms of boxes
8.1. The root system
Let
be an orthonormal basis of and view
elements
of as sequences
The root system of type is given by the sets
The simple roots are given by
The Weyl group
is the hyperoctahedral group of permutations of
such that
This groups acts on the by the rule
with the convention that
For this type C case there is a nice trick. View the root system as
with the convention that
In this notation and
This way the type C root system “looks like” a type A root system and many computations can be done in the same way as in type A.
8.5. Rearranging
We analyze the structure of the sets as considered in
(4.3). This corresponds to when the in the affine Hecke algebra is not a root of unity. The analysis in this case is analogous to the method
that was used in Section 5.11 to create books of placed configurations in the type A case.
Let Apply an element of the Weyl group to
to “arrange” the entries of so that, for each
Then
As in the type A case, the sets and
can be partitioned according to the cosets of the
elements of and it is sufficient to consider each separately and then
assemble the results in “books of pages.” There are three cases to consider:
Case The
Then
Case 1/2. The
Then
Case 0. The Then
It is notationally convenient to let
8.6. Boxes and standard tableaux
Let us assume that the entries of all lie in a single and describe the
resulting standard tableaux. The general case is obtained by creating books of pages of standard tableaux where the pages correspond to the different
of entries in
The placed configuration of boxes is determined as follows.
8.7. Case
Assume that is of the form
Place boxes on two pages of infinite graph paper. These pages are numbered and and
each page has the diagonals numbered consecutively with the elements of from bottom left to top right. View these
two pages, page and page as “linked.” For each
place on diagonal
of page and
on diagonal of page The boxes
on each diagonal are arranged in increasing order from top left to bottom right. The placement of boxes on page is a
rotation of the placement of the boxes on page
Using the notation for the root system of type in (8.4)
Note that
if and only if
and similarly
if and only if
If arrange the boxes on adjacent diagonals according to the rules
if place
northwest of and
if
place southeast of
A standard tableau is a negative rotationally symmetric filling of the boxes with
such that
if and and
are in the same diagonal,
if and
are in adjacent diagonals and is northwest of
if and
are in adjacent diagonals and is southeast of
The negative rotational symmetry means that the filling of the boxes on page is the same as the filling on page
except rotated by and with all entries in the boxes multiplied by
Example. Suppose and
and
The placed configuration of boxes corresponding to is
and a sample negative rotationally symmetric standard tableau is
8.8. Case 1/2
Assume that is of the form
Place boxes on a page of infinite graph paper which has its diagonals numbered consecutively with the elements of
from bottom left to top right. This page has page number
For each
place boxi on diagonal and
on diagonal
The boxes on each diagonal are arranged in
increasing order from top left to bottom right and the placement of boxes is negative rotationally symmetric in the sense that a
rotation takes boxi to
Using the root system notation in (8.4),
Note that it is the formulation of the root system of type in (8.4) which makes the description of
and
nice in this case. If
arrange the boxes on adjacent diagonals according to
the rules
if place
northwest of and
if
place southeast of
A standard tableau is a negative rotationally symmetric filling of the boxes with
such that
if and and
are in the same diagonal,
if and
are in adjacent diagonals and is northwest of
if and
are in adjacent diagonals and is southeast of
The negative rotational symmetry means that the filling of the boxes is the same if each entry is multiplied by and the
configuration is rotated by
Example. Suppose
and
The placed configuration of boxes corresponding to is as given below:
8.9. Case 0
Assume that is of the form
Place boxes on a page of infinite graph paper which has its diagonals numbered consecutively with the elements of
from bottom left to top right. This page has page number 0. For each
place on diagonal and
on diagonal
The boxes on each diagonal are arranged in increasing order from top left to bottom
right and the placement of boxes is negative rotationally symmetric in the sense that a rotation takes boxi to
Using the root system notation in (8.4),
If arrange the boxes on adjacent diagonals
according to the rules
if place
northwest of and
if
place southeast of
A standard tableau is a negative rotationally symmetric filling of the boxes with
such that
if and and
are in the same diagonal,
if and
are in adjacent diagonals and is northwest of
if and
are in adjacent diagonals and is southeast of
The negative rotational symmetry means that the filling of the boxes is the same if each entry is multiplied by and the
configuration is rotated by
Example. Suppose
The placed configuration of boxes corresponding to is as given below:
8.10.
A posteriori the analysis of the three cases
and 0, it becomes evident that the trick of using the formulation of the root system of type
in (8.4) provides a completely uniform description of the configurations of boxes and standard tableaux corresponding
to type local regions. All three cases give negative rotationally invariant tableaux. We could not ask for nature to
work out more perfectly.
Notes and References
This is an excerpt of the paper entitled Affine Hecke algebras and generalized standard Young tableaux written by Arun Ram in 2002, published in the
Academic Press Journal of Algebra 260 (2003) 367-415. The paper was dedicated to Robert Steinberg.
Research supported in part by the National Science Foundation (DMS-0097977) and the National Security Agency (MDA904-01-1-0032).