bug in Ext with yonedaExtension

[David Eisenbud]

In Ext.m2 in the new release, e=Ext(ZZ, Module, Module)

does not set 

e.cache.Ext

but yonedaExtension (Matrix)  (where Matrix is a map with target e) requires it.

For example,

i25 : S = ZZ/101[t]
i26 : M = coker vars S
i27 : e = Ext^1(M,M)
o27 = cokernel {-1} | t |
i28 : peek e.cache
o28 = CacheTable{cache => MutableHashTable{}}
                 pruningMap => {-1} | 1 |
i29 : yonedaExtension(e_{0})
stdio:62:15:(3): error: expected target of map to be an Ext^d(M,N) module

(Oddly, this bug doesn't show up unless you uninstallpackage "Complexes" and then

reinstall it, so two of my systems behaved differently).

--

David Eisenbud

Professor of Mathematics

University of California Berkeley

https://eisenbud.github.io/

[Mahrud Sayrafi]

I can't reproduce this issue yet. yonedaExtension is only defined in Complexes, and only works if the Ext module was computed using the routine in Complexes, so you would need to load Complexes first (or have set HomologicalAlgebraPackage = "Complexes" in init.m2).

Also, I don't think you need to install Complexes, which takes a long time, in order to use it. Is there a particular reason you install it first?

Mahrud

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