Given an ideal $I\subset{} R$, ``multiplicity I'' returns the degree of the normal cone of $I$. When $R/I$ has finite length this is the sum of the Samuel multiplicities of $I$ at the various localizations of $R$. When $I$ is generated by a complete intersection, this is the length of the ring $R/I$ but in general it is greater. For example,
i1 : R=ZZ/101[x,y] o1 = R o1 : PolynomialRing |
i2 : I = ideal(x^3, x^2*y, y^3) 3 2 3 o2 = ideal (x , x y, y ) o2 : Ideal of R |
i3 : multiplicity I o3 = 9 |
i4 : degree I o4 = 7 |
The normal cone is computed using the Rees algebra, thus may be slow.
The object multiplicity is a method function with options.