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D.15.5.10 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";
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);
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