D.4.8.4 computeConstant

Usage:

computeConstant(f,x); f number, x number

Assume:

f is a number in a rational function field, x is a variable of the field.

Return:

number, the constant coefficient of the Laurent series of f in the variable x.

Theory:

Computes the constant coefficient of the Laurent series by iterative differentiation.

LIB "ellipticcovers.lib";
ring R=(0,x1,x2,x3,x4),(q1,q2,q3,q4,q5,q6),dp;
graph G = makeGraph(list(1,2,3,4),list(list(1,3),list(1,2),list(1,2),list(2,4),list(3,4),list(3,4)));
number P = propagator(G,list(1,1,1,0,0,0));
computeConstant(P,x2);
==> (2*x1^6*x3^2+2*x1^2*x3^6)/(x3^8-4*x3^6*x4^2+6*x3^4*x4^4-4*x3^2*x4^6+x4^8)