Skip to main content
deleted 1 character in body
Source Link
T. Amdeberhan
  • 43.2k
  • 5
  • 57
  • 217

Orangeskid's guess is correct: a more general fact holds that the binomial transform preserves Hankel determinants.

For a matrix $(a_{ij})$ (it is convenient to enumerate rows and columns from 0,not from 1) denote $$b_{ij}=\sum_{k, s}{i\choose k}{j\choose s}a_{ks}.$$ This matrix transform corresponds to a left and right multiplicaton by unitriangular matrices, thus it preserves determinant. Now if $a_{ij}=f(i+j)$ is a Hankel matrix, then $$b_{ij}=\sum_t f(t)\sum_{k+s=t} {i\choose k}{j\choose s}=\sum_tf(t){i+j\choose t}$$ is a Hankel matrix corresponding to the binomial transform of $f$.

It remains to remindsrecall that $n! =\sum_k {n\choose k} d_k$ (combinatorially ${n\choose k} d_k$ counts the number of permutations of $\{1,\ldots, n\}$ with exactly $n-k$ fixed points, thus this formula), that means that the sequence of factorials is the binomial transform of the sequence of dearrangements.

Orangeskid's guess is correct: a more general fact holds that the binomial transform preserves Hankel determinants.

For a matrix $(a_{ij})$ (it is convenient to enumerate rows and columns from 0,not from 1) denote $$b_{ij}=\sum_{k, s}{i\choose k}{j\choose s}a_{ks}.$$ This matrix transform corresponds to a left and right multiplicaton by unitriangular matrices, thus it preserves determinant. Now if $a_{ij}=f(i+j)$ is a Hankel matrix, then $$b_{ij}=\sum_t f(t)\sum_{k+s=t} {i\choose k}{j\choose s}=\sum_tf(t){i+j\choose t}$$ is a Hankel matrix corresponding to the binomial transform of $f$.

It remains to reminds that $n! =\sum_k {n\choose k} d_k$ (combinatorially ${n\choose k} d_k$ counts the number of permutations of $\{1,\ldots, n\}$ with exactly $n-k$ fixed points, thus this formula), that means that the sequence of factorials is the binomial transform of the sequence of dearrangements.

Orangeskid's guess is correct: a more general fact holds that the binomial transform preserves Hankel determinants.

For a matrix $(a_{ij})$ (it is convenient to enumerate rows and columns from 0,not from 1) denote $$b_{ij}=\sum_{k, s}{i\choose k}{j\choose s}a_{ks}.$$ This matrix transform corresponds to a left and right multiplicaton by unitriangular matrices, thus it preserves determinant. Now if $a_{ij}=f(i+j)$ is a Hankel matrix, then $$b_{ij}=\sum_t f(t)\sum_{k+s=t} {i\choose k}{j\choose s}=\sum_tf(t){i+j\choose t}$$ is a Hankel matrix corresponding to the binomial transform of $f$.

It remains to recall that $n! =\sum_k {n\choose k} d_k$ (combinatorially ${n\choose k} d_k$ counts the number of permutations of $\{1,\ldots, n\}$ with exactly $n-k$ fixed points, thus this formula), that means that the sequence of factorials is the binomial transform of the sequence of dearrangements.

added 308 characters in body
Source Link
Fedor Petrov
  • 108.9k
  • 9
  • 264
  • 459

Orangeskid's guess is correct: a more general fact holds that the binomial transform preserves Hankel determinants.

For a matrix $(a_{ij})$ (it is convenient to enumerate rows and columns from 0,not from 1) denote $$b_{ij}=\sum_{k, s}{i\choose k}{j\choose s}a_{ks}.$$ This matrix transform corresponds to a left and right multiplicaton by unitriangular matrices, thus it preserves determinant. Now if $a_{ij}=f(i+j)$ is a Hankel matrix, then $$b_{ij}=\sum_t f(t)\sum_{k+s=t} {i\choose k}{j\choose s}=\sum_tf(t){i+j\choose t}$$ is a Hankel matrix corresponding to the binomial transform of $f$.

It remains to reminds that $n! =\sum_k {n\choose k} d_k$ (combinatorially ${n\choose k} d_k$ counts the number of permutations of $\{1,\ldots, n\}$ with exactly $n-k$ fixed points, thus this formula), that means that the sequence of factorials is the binomial transform of the sequence of dearrangements.

Orangeskid's guess is correct: a more general fact holds that the binomial transform preserves Hankel determinants.

For a matrix $(a_{ij})$ (it is convenient to enumerate rows and columns from 0,not from 1) denote $$b_{ij}=\sum_{k, s}{i\choose k}{j\choose s}a_{ks}.$$ This matrix transform corresponds to a left and right multiplicaton by unitriangular matrices, thus it preserves determinant. Now if $a_{ij}=f(i+j)$ is a Hankel matrix, then $$b_{ij}=\sum_t f(t)\sum_{k+s=t} {i\choose k}{j\choose s}=\sum_tf(t){i+j\choose t}$$ is a Hankel matrix corresponding to the binomial transform of $f$.

Orangeskid's guess is correct: a more general fact holds that the binomial transform preserves Hankel determinants.

For a matrix $(a_{ij})$ (it is convenient to enumerate rows and columns from 0,not from 1) denote $$b_{ij}=\sum_{k, s}{i\choose k}{j\choose s}a_{ks}.$$ This matrix transform corresponds to a left and right multiplicaton by unitriangular matrices, thus it preserves determinant. Now if $a_{ij}=f(i+j)$ is a Hankel matrix, then $$b_{ij}=\sum_t f(t)\sum_{k+s=t} {i\choose k}{j\choose s}=\sum_tf(t){i+j\choose t}$$ is a Hankel matrix corresponding to the binomial transform of $f$.

It remains to reminds that $n! =\sum_k {n\choose k} d_k$ (combinatorially ${n\choose k} d_k$ counts the number of permutations of $\{1,\ldots, n\}$ with exactly $n-k$ fixed points, thus this formula), that means that the sequence of factorials is the binomial transform of the sequence of dearrangements.

added 35 characters in body
Source Link
Fedor Petrov
  • 108.9k
  • 9
  • 264
  • 459

Orangeskid's guess is correct: a more general fact holds that the binomial transform preserves Hankel determinants.

For a matrix $(a_{ij})$ (it is convenient to enumerate rows and columns from 0,not from 1) denote $$b_{ij}=\sum_{k, s}{i\choose k}{j\choose s}a_{ks}.$$ This matrix transform corresponds to a left and right multiplicaton by unitriangular matrices, thus it preserves determinant. Now if $a_{ij}=f(i+j)$ is a Hankel matrix, then $$b_{ij}=\sum_t f(t)\sum_{k+s=t} {i\choose k}{j\choose s}=\sum_tf(t){i+j\choose t}$$ is a Hankel matrix corresponding to the binomial transform of $f$.

Orangeskid's guess is correct: binomial transform preserves Hankel determinants.

For a matrix $(a_{ij})$ (it is convenient to enumerate rows and columns from 0,not from 1) denote $$b_{ij}=\sum_{k, s}{i\choose k}{j\choose s}a_{ks}.$$ This matrix transform corresponds to a left and right multiplicaton by unitriangular matrices, thus it preserves determinant. Now if $a_{ij}=f(i+j)$ is a Hankel matrix, then $$b_{ij}=\sum_t f(t)\sum_{k+s=t} {i\choose k}{j\choose s}=\sum_tf(t){i+j\choose t}$$ is a Hankel matrix corresponding to the binomial transform of $f$.

Orangeskid's guess is correct: a more general fact holds that the binomial transform preserves Hankel determinants.

For a matrix $(a_{ij})$ (it is convenient to enumerate rows and columns from 0,not from 1) denote $$b_{ij}=\sum_{k, s}{i\choose k}{j\choose s}a_{ks}.$$ This matrix transform corresponds to a left and right multiplicaton by unitriangular matrices, thus it preserves determinant. Now if $a_{ij}=f(i+j)$ is a Hankel matrix, then $$b_{ij}=\sum_t f(t)\sum_{k+s=t} {i\choose k}{j\choose s}=\sum_tf(t){i+j\choose t}$$ is a Hankel matrix corresponding to the binomial transform of $f$.

added 51 characters in body
Source Link
Fedor Petrov
  • 108.9k
  • 9
  • 264
  • 459
Loading
Source Link
Fedor Petrov
  • 108.9k
  • 9
  • 264
  • 459
Loading