D.15.5.4 negativedivisor

Usage:

negativedivisor(A); A*(-1); A = divisor.

Assume:

A is a divisor on X.

Return:

a divisor on X

Theory:

The procedure will interchange the numerator and denominator ideals.

LIB "divisors.lib";
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));
A;
divisor D = negativedivisor(A);
D;