bug in new version: random maps go in wrong direction

[David Eisenbud]

I installed, with Brew, the new version of M2, and found that one of my packages

wouldn't work. I think the direction of the morphism produced by

(random, Module, Module)

now goes the other way from what it did.

 Here's a snippet:

+ M2 --no-readline --print-width 112
Macaulay2, version 1.25.05
......

i22 : S = ZZ/101[t]
o22 = S
o22 : PolynomialRing
i23 : M = S^1/t
o23 = cokernel | t |

                                         1
o23 : S-module, quotient of S
i24 : random(M,S^1)
o24 = 0
                   1
o24 : Matrix S  <-- M

---

What it says in the

documentation:

• Usage:
• f = random(F, G)
• Inputs:
  • F, a module,
  • G, a module,
  • .....
  • Outputs:
  • f, a matrix, a random, graded, degree 0 map f:G→F

--

David Eisenbud

Professor of Mathematics

University of California Berkeley

https://eisenbud.github.io/

[Mahrud Sayrafi]

Ah, that's a bug that was introduced recently. Here is the workaround:

random' = (F, G) -> homomorphism random Hom(G, F, DegreeLimit => 0)

random'(S^1, M)

The bug was calling Hom(F, G) instead of Hom(G, F) ...

I just opened a pull request and requested a review from you here.

Mahrud

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