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jakobkroeker / M2

The primary source code repository for Macaulay2
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primary decomposition: hard example for ShimoyamaYokoyama strategy #42

Open jakobkroeker opened 10 years ago

jakobkroeker commented 10 years ago 
restart
rng = QQ[x,y,z]
I = ideal(4*y*z-(1/2)*z,(1/2)*x*y*z+4*z^3+2*x*z,-(5/2)*z^2-z-1)
 -- does not finish in reasonable time:
pd = primaryDecomposition( I, Strategy=>ShimoyamaYokoyama );
mikestillman commented 10 years ago

I'm a bit surprised: the problem here is that decompose is returning an empty list. We had this problem some time ago, the issue is (at first look) the fractions. If you instead decompose 2*I, it gives a nonempty list. I thought this was fixed, and also that there are tests for it. I obviously must be mistaken!

DanGrayson commented 10 years ago

The empty list is correctly returned, but incorrectly handled, and the error message could be better:

i6 : monomialIdeal {} stdio:6:1:(3): error: expected a polynomial ring without quotient elements

The error message should say "monomialIdeal: expected a nonempty list".

mikestillman commented 10 years ago

What do you mean that the empty list is correctly returned? That should not be correct?

DanGrayson commented 10 years ago

I seem to recall it was decomposing the unit ideal, so it is correct.

jakobkroeker commented 9 years ago

seems fixed now. Add a test (or is there one?