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Statistic identifier: St000319

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Collection: Integer partitions

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Description: The spin of an integer partition.

The Ferrers shape of an integer partition $\lambda$ can be decomposed into border strips. The spin is then defined to be the total number of crossings of border strips of $\lambda$ with the vertical lines in the Ferrers shape.

The following example is taken from Appendix B in [1]: Let $\lambda = (5,5,4,4,2,1)$. Removing the border strips successively yields the sequence of partitions
$$(5,5,4,4,2,1), (4,3,3,1), (2,2), (1), ().$$
The first strip $(5,5,4,4,2,1) \setminus (4,3,3,1)$ crosses $4$ times, the second strip $(4,3,3,1) \setminus (2,2)$ crosses $3$ times, the strip $(2,2) \setminus (1)$ crosses $1$ time, and the remaining strip $(1) \setminus ()$ does not cross.
This yields the spin of $(5,5,4,4,2,1)$ to be $4+3+1 = 8$.

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References: [1] ,  Loehr, N. A., Warrington, G. S. Nested quantum Dyck paths and $\nabla (s_\lambda )$ [[MathSciNet:2418288]] [[arXiv:0705.4608]]
[2]   Haglund, J. The $q$,$t$-Catalan numbers and the space of diagonal harmonics [[MathSciNet:2371044]]

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Code:
def remove_border_strip(L):
    return Partition( part-1 for part in L[1:] if part > 1 )

def border_strip_decomposition(L):
    decomp = []
    while len(L) > 0:
        decomp.append(L)
        L = remove_border_strip(L)
    return decomp

def border_strip_crossing_number(L):
    L = list(L)+[1]
    return sum( L[i-1]-L[i] for i in range(1,len(L)) )

def statistic(L):
    return sum( border_strip_crossing_number(X) for X in border_strip_decomposition(L) )

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Statistic values:

[1]                   => 0
[2]                   => 1
[1,1]                 => 0
[3]                   => 2
[2,1]                 => 1
[1,1,1]               => 0
[4]                   => 3
[3,1]                 => 2
[2,2]                 => 1
[2,1,1]               => 1
[1,1,1,1]             => 0
[5]                   => 4
[4,1]                 => 3
[3,2]                 => 2
[3,1,1]               => 2
[2,2,1]               => 1
[2,1,1,1]             => 1
[1,1,1,1,1]           => 0
[6]                   => 5
[5,1]                 => 4
[4,2]                 => 3
[4,1,1]               => 3
[3,3]                 => 3
[3,2,1]               => 2
[3,1,1,1]             => 2
[2,2,2]               => 1
[2,2,1,1]             => 1
[2,1,1,1,1]           => 1
[1,1,1,1,1,1]         => 0
[7]                   => 6
[6,1]                 => 5
[5,2]                 => 4
[5,1,1]               => 4
[4,3]                 => 4
[4,2,1]               => 3
[4,1,1,1]             => 3
[3,3,1]               => 3
[3,2,2]               => 2
[3,2,1,1]             => 2
[3,1,1,1,1]           => 2
[2,2,2,1]             => 1
[2,2,1,1,1]           => 1
[2,1,1,1,1,1]         => 1
[1,1,1,1,1,1,1]       => 0
[8]                   => 7
[7,1]                 => 6
[6,2]                 => 5
[6,1,1]               => 5
[5,3]                 => 5
[5,2,1]               => 4
[5,1,1,1]             => 4
[4,4]                 => 5
[4,3,1]               => 4
[4,2,2]               => 3
[4,2,1,1]             => 3
[4,1,1,1,1]           => 3
[3,3,2]               => 3
[3,3,1,1]             => 3
[3,2,2,1]             => 2
[3,2,1,1,1]           => 2
[3,1,1,1,1,1]         => 2
[2,2,2,2]             => 1
[2,2,2,1,1]           => 1
[2,2,1,1,1,1]         => 1
[2,1,1,1,1,1,1]       => 1
[1,1,1,1,1,1,1,1]     => 0
[9]                   => 8
[8,1]                 => 7
[7,2]                 => 6
[7,1,1]               => 6
[6,3]                 => 6
[6,2,1]               => 5
[6,1,1,1]             => 5
[5,4]                 => 6
[5,3,1]               => 5
[5,2,2]               => 4
[5,2,1,1]             => 4
[5,1,1,1,1]           => 4
[4,4,1]               => 5
[4,3,2]               => 4
[4,3,1,1]             => 4
[4,2,2,1]             => 3
[4,2,1,1,1]           => 3
[4,1,1,1,1,1]         => 3
[3,3,3]               => 3
[3,3,2,1]             => 3
[3,3,1,1,1]           => 3
[3,2,2,2]             => 2
[3,2,2,1,1]           => 2
[3,2,1,1,1,1]         => 2
[3,1,1,1,1,1,1]       => 2
[2,2,2,2,1]           => 1
[2,2,2,1,1,1]         => 1
[2,2,1,1,1,1,1]       => 1
[2,1,1,1,1,1,1,1]     => 1
[1,1,1,1,1,1,1,1,1]   => 0
[10]                  => 9
[9,1]                 => 8
[8,2]                 => 7
[8,1,1]               => 7
[7,3]                 => 7
[7,2,1]               => 6
[7,1,1,1]             => 6
[6,4]                 => 7
[6,3,1]               => 6
[6,2,2]               => 5
[6,2,1,1]             => 5
[6,1,1,1,1]           => 5
[5,5]                 => 7
[5,4,1]               => 6
[5,3,2]               => 5
[5,3,1,1]             => 5
[5,2,2,1]             => 4
[5,2,1,1,1]           => 4
[5,1,1,1,1,1]         => 4
[4,4,2]               => 5
[4,4,1,1]             => 5
[4,3,3]               => 4
[4,3,2,1]             => 4
[4,3,1,1,1]           => 4
[4,2,2,2]             => 3
[4,2,2,1,1]           => 3
[4,2,1,1,1,1]         => 3
[4,1,1,1,1,1,1]       => 3
[3,3,3,1]             => 3
[3,3,2,2]             => 3
[3,3,2,1,1]           => 3
[3,3,1,1,1,1]         => 3
[3,2,2,2,1]           => 2
[3,2,2,1,1,1]         => 2
[3,2,1,1,1,1,1]       => 2
[3,1,1,1,1,1,1,1]     => 2
[2,2,2,2,2]           => 1
[2,2,2,2,1,1]         => 1
[2,2,2,1,1,1,1]       => 1
[2,2,1,1,1,1,1,1]     => 1
[2,1,1,1,1,1,1,1,1]   => 1
[1,1,1,1,1,1,1,1,1,1] => 0

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Created: Dec 08, 2015 at 17:15 by Christian Stump

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Last Updated: Dec 17, 2015 at 11:19 by Christian Stump