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The S_4 character table by rim-hook recursion
Example
The Murnaghan–Nakayama rule (The Murnaghan–Nakayama character rule) computes the full ordinary character table of . With rows and columns the classes (of sizes ),
(for example on the -cycle class is because is not a hook (The value of an irreducible character on a full cycle is supported on hooks), and , by the same rule). Checking the first orthogonality relation (The first orthogonality relation for irreducible complex characters) row by row gives, for instance, , and every row has norm .
Facts & Assumptions
Given: The partitions of , the conjugacy classes of indexed by cycle type with sizes (The conjugacy classes of are indexed by the tuples with , If has cycles of length , then ), and for every partition of an integer the character of the complex Specht module (Column antisymmetrizers, polytabloids, and Specht modules).
Murnaghan–Nakayama rule: for a cycle of length on a specified set of points fixed by (a specified fixed point for length ), , summed over the removable border strips of of size , the empty sum being (The Murnaghan–Nakayama character rule).
Hook lengths and dimensions: the hook lengths of are ; ; ; , and the dimensions are , namely for (Hook, arm, leg, and hook length of a box, The hook length formula).
The five conjugacy classes of have cycle types and sizes (The conjugacy classes of are indexed by the tuples with , If has cycles of length , then , Support, fixed points, disjoint cycles, cycle length, disjoint-cycle decompositions, and cycle type).
Standard inner product (The standard inner product on ), and the first orthogonality relation for irreducible characters (The first orthogonality relation for irreducible complex characters); the character table of a finite group has rows the irreducible characters and columns the classes (The character table of a finite group).
For the empty partition is the trivial character of , so (Column antisymmetrizers, polytabloids, and Specht modules).
Verification
Row : for each part of the cycle type the unique removable -strip of the row is horizontal and has height , leaving the row , so iterating the rule [F1] gives on all five classes. Row is the sign character: the unique -strip of the column is vertical of height , so iterating [F1] gives for the parts of the cycle type, that is the values on .
Row : by [F2] the dimension is ; on the only -strip removes the domino and leaves with height , so the value is ; on the same strip gives ; on the hook lengths contain no , so there is no -strip and the value is ; on the whole diagram is the unique -strip, of height , so the value is . This gives the row .
Row : the two -strips are the bottom row to (height ) and the right column to (height ), so on the value is , on it is ; on the unique -strip (leaving the single node ) has height and gives ; on the hook lengths contain no , so the value is ; the dimension is by [F2]. Row : the unique -strip removes the vertical domino and leaves with height , so the values on and are and ; there is no -strip because the hook lengths are ; the whole diagram is the unique -strip, of height , giving on ; the dimension is by [F2]. This gives the rows and .
With the class sizes [F3] and the standard inner product [F4], the five rows have norms for and , for and , and for ; pairwise orthogonality holds as in the displayed computation , and likewise , the remaining pairs checking in the same way. Hence the five rows computed by the recursion are exactly the character table of displayed in the statement, with the rows orthonormal with respect to the class sizes of [F3].
Remarks
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The -cycle column is the hook column. On the class only the hooks can be nonzero and their values are , while ; this is the S_4 instance of the full-cycle lemma The value of an irreducible character on a full cycle is supported on hooks.
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Cross-check. The same array is obtained by the fixed-tabloid algorithm of Fixed-tabloid reconstruction of the character table (Fox–Mullineux), whose worked instance in the source recorded above produces the identical entries; the two routes use disjoint inputs, the recursion using hooks and the fixed-tabloid route using the Gram equation.
Depends on
- The Murnaghan–Nakayama character rule
- The first orthogonality relation for irreducible complex characters
- The character table of a finite group
- The standard inner product on $\mathrm{cf}(G)$
- The hook length formula
- Hook, arm, leg, and hook length of a box
- The value of an irreducible character on a full cycle is supported on hooks
- The conjugacy classes of $S_n$ are indexed by the tuples $(c_1,\ldots,c_n)$ with $\sum k c_k=n$
- If $\sigma\in S_n$ has $c_k$ cycles of length $k$, then $|C_{S_n}(\sigma)|=\prod_{k=1}^n k^{c_k}c_k!$
- Column antisymmetrizers, polytabloids, and Specht modules
- Support, fixed points, disjoint cycles, cycle length, disjoint-cycle decompositions, and cycle type
Used by
Nothing in the library uses this result yet.
Dependency tree · two levels
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Sources
- G. D. James, The Representation Theory of the Symmetric Groups, Lecture Notes in Mathematics 682, Springer 1978 (complete author-hosted scan, 161 pp.) (standard reference, not scraped)
- William Woods, Representation theory of the symmetric groups (Cambridge Part III essay, 33 pp.) (standard reference, not scraped)
- I. G. Macdonald, Symmetric Functions and Hall Polynomials, 2nd ed., Oxford Mathematical Monographs, 1995 (complete author-hosted scan, 486 pp.) (standard reference, not scraped)