Matrix TP: counting ab core by Corner
Wang and Yang: Narayana matrix is TP.
Huang and Wang: n,n+1-core counted by corner is Narayana.
What about n,kn+a-core?
First we check n,n+1 cores counted by #corners:
1
1
1 1
1 3 1
1 6 6 1
1 10 20 10 1
1 15 50 50 15 1
this is Narayana numbers all right, and TP.
Now n,2n+1 cores. Fuss-Catalan case!
[ 1 0 0 0 0 0 0 0 0 0 0 0 0]
[ 1 0 0 0 0 0 0 0 0 0 0 0 0]
[ 1 1 1 0 0 0 0 0 0 0 0 0 0]
[ 1 3 5 2 1 0 0 0 0 0 0 0 0]
[ 1 6 16 16 12 3 1 0 0 0 0 0 0]
[ 1 10 40 70 79 46 22 4 1 0 0 0 0]
[ 1 15 85 225 365 351 245 100 35 5 1 0 0]
[ 1 21 161 595 1323 1841 1801 1176 590 185 51 6 1]
Minimal minors of all sizes:
0 1
1 0
2 0
3 0
4 0
5 0
6 0
7 0
So we can safely conjecture that this is part of an infinite TP matrix.
More Fuss-Catalan case. n,2n-1 case!
result:
[ 1 0 0 0 0 0 0 0 0 0 0 0 0 0]
[ 1 0 0 0 0 0 0 0 0 0 0 0 0 0]
[ 1 1 0 0 0 0 0 0 0 0 0 0 0 0]
[ 1 3 2 1 0 0 0 0 0 0 0 0 0 0]
[ 1 6 10 9 3 1 0 0 0 0 0 0 0 0]
[ 1 10 30 45 34 18 4 1 0 0 0 0 0 0]
[ 1 15 70 160 201 165 80 30 5 1 0 0 0 0]
[ 1 21 140 455 840 1001 776 435 155 45 6 1 0 0]
[ 1 28 252 1106 2800 4578 5048 3997 2226 945 266 63 7 1]
Minors of sizes<=8 are all non-negative.
We skip n, kn+a type here. Rest assured that n,3n-1 is checked, to say the least.
What people don't often realize is that we may also consider 2n-1, 3n-1 cores.
This is where things go wrong.
[ 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0]
[ 1 3 2 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0]
[ 1 10 19 21 17 14 9 5 2 1 0 0 0 0 0 0 0 0 0 0 0 0]
[ 1 21 85 178 260 308 291 237 164 107 57 33 16 7 2 1 0 0 0 0 0 0]
[ 1 36 256 896 2051 3501 4700 5290 5112 4423 3395 2430 1552 922 493 264 117 56 23 9 2 1]
In row [2, 3, 4] and column [8, 9, 10] we have the following submatrix
[ 2 1 0]
[ 164 107 57]
[5112 4423 3395]
with determinant -43088. Sucks!
Again we look at the n,2n-1 case. We check out the columns.
The first column 1,1,1...
is constant. The second 1,3,6,10
is the choose-2 binomial number.
The third is 2*binomial(n,4).
The fourth col does not seem polynomial at first:
[0, 0, 0, 1, 9, 45, 160, 455, 1106, 2394
but it is infact a pol of degree 6.