Re: [Macaulay2] Issue with resolution in M2 1.6

[Michael Stillman]

Hi Brett,

Hmm, you are right.  I had fixed a bug in that code recently, but perhaps the bug fix caused some other issue.  I'll take a look.

Thanks!

Mike

On May 16, 2013, at 7:42 PM, Brett Barwick <bbar...@uscupstate.edu> wrote:

Hello,

While Branden Stone and I were running some examples for our QuillenSuslin package, we came across the following example in which the desired free resolution is computed very quickly in M2 v1.5 but seems not to run as well in v1.6:

R = ZZ[x,y]

f = matrix{{x^3,3*y+1,y^3+2*x*y^2}}

P = minimalPresentation ker f

res P

The command `res P' completes in .016 seconds in M2 v1.5, but we stopped the computation in v1.6 after it ran for 5 minutes with no result.

Any thoughts about what might be causing this?

Thanks,

Brett

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[mike stillman]

Dear Brett,

minimalPresentation doesn't work so well for inhomogeneous input (in part, because there is no unique minimal presentation).  

In this example, there is a workaround: if you replace the line "ker f" with "trim ker f", then a reasonable answer results.  I have opened an issue on our M2 github to fix minimalPresentation for modules over ZZ.

Best,

Mike

On Thursday, May 16, 2013 11:00:40 PM UTC-4, mike stillman wrote:

Hi Brett,

Hmm, you are right.  I had fixed a bug in that code recently, but perhaps the bug fix caused some other issue.  I'll take a look.

Thanks!

Mike