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allNefContractions -- produces all contractions corresponding to each face in the nef cone

Description

This method chooses a vector in the relative interior of every face of the nef cone and produces the corresponding map.

i1 : X = hirzebruchSurface 1;
i2 : L = allNefContractions X

o2 = {| 1 0 |, | 1 0 |, | 1 0 |}
               | 0 1 |  | 0 1 |

o2 : List
i3 : assert(all(L, phi -> isWellDefined phi))

Caveat

This method is exponential in the number of rays of the fan, so the runtime may be quite long!

See also

Ways to use allNefContractions:

  • allNefContractions(NormalToricVariety)

For the programmer

The object allNefContractions is a method function.


The source of this document is in /build/reproducible-path/macaulay2-1.25.06+ds/M2/Macaulay2/packages/ToricHigherDirectImages.m2:822:0.