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EvalBinExp

binomial expansion functions

Syntax
EvalBinExp(B:TAGGED("$binrepr.BinExp"), Up:INT, Down:INT):INT

where N and K are positive integers, and Up and Down are integers.

Description
The function BinExp computes the K-binomial expansion of N, i.e., the unique expression
  N = binomial(N(K),K) + binomial(N(K-1),K-1) + ... + binomial(N(I),I)
where N(K) > ... > N(I) >= 1, for some I.

This function computes the sum of the binomial coefficients appearing in the K-binomial expansion of N after replacing each summand binomial(N(J),J) by binomial(N(J)+Up,J+Down). It is useful in generalizations of Macaulay's theorem characterizing Hilbert functions.

It is the same as BinExp with 4 arguments except it takes a precomputed binomial expansion as an argument rather than N and K.

Example
/**/  BE := BinExp(13,4);
/**/  BE;
Bin(5,4) + Bin(4,3) + Bin(3,2) + Bin(1,1)

/**/  EvalBinExp(BE,1,1);
16

  BinExp(13,4,1,1);
16
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See Also