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D.15.11.10 effective

Procedure from library divisors.lib (see divisors_lib).

Usage:
effective(A); A = divisor.

Assume:
A is a divisor on X which is linearly equivalent to an effective divisor.

Return:
divisor on X.

Theory:
We compute an effective divisor linearly equivalent to A.

Example:
 
LIB "divisors.lib";
==> Welcome to polymake version
==> Copyright (c) 1997-2015
==> Ewgenij Gawrilow, Michael Joswig (TU Darmstadt)
==> http://www.polymake.org
ring r=31991,(x,y,z),dp;
ideal I = y^2*z - x*(x-z)*(x+3*z);
qring Q = std(I);
divisor A = makeDivisor(ideal(x,z),ideal(1));
divisor B = makeDivisor(ideal(x,y),ideal(1));
divisor D = divisorplus(multdivisor(2,B),negativedivisor(A));
effective(D);
==> (z,x) - (1)
==>