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D.15.6.13 formaldivisorplus

Procedure from library divisors.lib (see divisors_lib).

Usage:
formaldivisorplus(A ,B); A + B; A = formaldivisor, B = formaldivisor.

Assume:
A and B are formal divisors on X.

Return:
a formal divisor on X

Theory:
The procedure will add the formal sums.

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 C = makeDivisor(ideal(x-z,y),ideal(1));
formaldivisor fE= makeFormalDivisor(list(list(-5,A),list(2,B)));
formaldivisor fE2= makeFormalDivisor(list(list(-5,A),list(2,C)));
formaldivisorplus(fE,fE2);