HeuristicDecomposition fails for Prym

[edgarcosta]

AttachSpec("~/CHIMP/CHIMP.spec");
SetVerbose("EndoFind", 0);
SetVerbose("CurveRec", 0);
P<x,y,z>:=ProjectiveSpace(RationalsExtra(6000),2);
C:=Curve(P,x^4 - 6*x^3*z + 11*x^2*z^2 - 4*y^3*z - 6*x*z^3 + 12*y^2*z^2 - 8*y*z^3);
PC := PeriodMatrix(C);
SetVerbose("EndoFind", 1);
SetVerbose("CurveRec", 2);
foo := HeuristicDecomposition(C);

Calculating period matrix...
using stored period matrix.

Finding geometric homomorphisms...
done finding geometric homomorphisms.

Finding number field defined by endomorphisms...
done finding number field defined by endomorphisms:
Rational Field

Calculating period matrix...
using stored period matrix.

Calculating period matrix...
using stored period matrix.

Calculating period matrix...
using stored period matrix.

Frobenius form of induced polarization:
[ 0  1  0  0]
[-1  0  0  0]
[ 0  0  0  2]
[ 0  0 -2  0]

Minkowski reduction...
done.

Integral reduction...
done.

Gottschling reduction...
done.

Minkowski reduction...
done.

Integral reduction...
done.

Gottschling reduction...
done.

Eigenvalues of imaginary part of reduced tau:
[ 1.2383, 1.9478 ]

Calculating theta derivatives...
done calculating theta derivatives.

Identifying correct twist...

Finding geometric homomorphisms...
done finding geometric homomorphisms.
Runtime error: No geometric homomorphism to original matrix found. Try increasing the precision.