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D.15.6.4 negativedivisor

Procedure from library divisors.lib (see divisors_lib).

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.

Example:
 
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;