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D.15.8.4 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;
==> (z,x) - (1)
==>
divisor D = negativedivisor(A);
D;
==> (1) - (z,x)
==>
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