This function returns the h-vector of the ring R, i.e., the
coefficients of the numerator of the simplified Poincare series for R.
The weights of the indeterminates of the current ring must all be 1,
and the coefficient ring must be a field.
If the input is not homogeneous, the Hilbert function of the
corresponding leading term (initial) ideal or module is calculated.
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Use R ::= Q[t,x,y,z];
HVector(R/Ideal(x,y,z)^5);
[1, 3, 6, 10, 15]
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Poincare(R/Ideal(x,y,z)^5);
(1 + 3t + 6t^2 + 10t^3 + 15t^4) / (1-t)
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