We say a symmetric divisor on M0,n is a symmetric F-divisor if D . FI1,I2,I3,I4 ≥0 for every F curve.
In the example below, we see that for n=8, the divisor 3B2+2B3+4B4 is a symmetric F-divisor, while the divisor B2 is not.
i1 : D=symmetricDivisorM0nbar(8,3*B_2+2*B_3+4*B_4) o1 = SymmetricDivisorM0nbar{2 => 3 } 3 => 2 4 => 4 NumberOfPoints => 8 o1 : SymmetricDivisorM0nbar |
i2 : isSymmetricFDivisor(D) o2 = true |
i3 : D=symmetricDivisorM0nbar(8,B_2) o3 = SymmetricDivisorM0nbar{2 => 1 } NumberOfPoints => 8 o3 : SymmetricDivisorM0nbar |
i4 : isSymmetricFDivisor(D) This divisor has negative intersection with the F curve F_{3, 2, 2, 1} (and maybe others too) o4 = false |