Macaulay2 » Documentation
Packages » Divisor :: toWeilDivisor
next | previous | forward | backward | up | index | toc

toWeilDivisor -- create a Weil divisor from a Q or R-divisor



Given a divisor with rational or real coefficients, but whose coefficients are actually integers, we first check if all coefficients are integers. If so we make this Weil divisor. Otherwise, an error is thrown.

i1 : R=QQ[x];
i2 : D=divisor({3/2}, {ideal(x)}, CoefficientType=>QQ)

o2 = 3/2*Div(x)

o2 : QWeilDivisor on R
i3 : E=divisor({1.5}, {ideal(x)}, CoefficientType=>RR)

o3 = 1.5*Div(x)

o3 : RWeilDivisor on R
i4 : toWeilDivisor(2*D)

o4 = 3*Div(x)

o4 : WeilDivisor on R
i5 : toWeilDivisor(2*E)

o5 = 3*Div(x)

o5 : WeilDivisor on R
i6 : isWeilDivisor(D)

o6 = false
i7 : try toWeilDivisor(D) then print "converted to a WeilDivisor" else print "can't be converted to a WeilDivisor"
can't be converted to a WeilDivisor

Notice in the final computation, D cannot be converted into a Weil divisor since $D$ has non-integer coefficients, but 2*D can be converted into a Weil divisor.

See also

Ways to use toWeilDivisor :

For the programmer

The object toWeilDivisor is a method function.