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LeanPool.NandakumarRamanaRao.NRR.PrimePolyhedron.FoxNeuwirth.RelativeSubdivisionCylinderCombinatorics

Recursive one-step subdivision cylinders #

This module gives the explicit finite cell and vertex formulas for the relative triangulation of Delta d x I whose lower boundary is the coarse simplex and whose upper boundary is its first barycentric subdivision.

The construction is recursive. Triangulate the boundary of the prism by one coarse lower simplex, all barycentric top simplices, and recursively triangulated side cylinders. Every boundary simplex is then coned to the central point (barycenter, 1 / 2).

Top cells of the recursive cone triangulation of Delta d x I.

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    A cell coned from a recursively triangulated side face.

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      The central cone point.

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        Coarse lower-boundary vertex.

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          Barycentric upper-boundary vertex.

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            Ordered vertices of a recursive cylinder cell.

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              @[simp]

              Spatial barycentric interpolation of a recursive cylinder cell.

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                Time barycentric interpolation of a recursive cylinder cell.

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                  Affine chart of one recursive one-step cylinder cell.

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                    Every spatial coordinate is the barycentric interpolation of declared vertices.

                    The time coordinate is the barycentric interpolation of declared vertex times.

                    @[simp]
                    theorem NRR.FoxNeuwirthOrderComplex.RelativeSubdivisionCylinderCombinatorics.timePoint_side (d : ℕ) (k : Fin (d + 2)) (q : Cell d) (w : ↑(SphereOddDegree.AffineBarycentricSubdivision.Delta (d + 2))) :
                    ↑(timePoint (d + 1) (sideCell d k q) w) = w 0 / 2 + ∑ i : Fin (d + 2), w i.succ * ↑(vertex d q i).2

                    Pairwise distinct vertices follow from injectivity of the affine chart.

                    theorem NRR.FoxNeuwirthOrderComplex.RelativeSubdivisionCylinderCombinatorics.lowerFacet_classification (d : ℕ) (q : Cell d) (j : Fin (d + 2)) (h : ∀ (i : Fin (d + 1)), ↑(vertex d q (j.succAbove i)).2 = 0) :
                    q = lowerCell d ∧ j = 0

                    A facet is entirely at time zero exactly for the coarse lower base facet.

                    theorem NRR.FoxNeuwirthOrderComplex.RelativeSubdivisionCylinderCombinatorics.upperFacet_classification (d : ℕ) (q : Cell d) (j : Fin (d + 2)) (h : ∀ (i : Fin (d + 1)), ↑(vertex d q (j.succAbove i)).2 = 1) :
                    j = 0 ∧ ∃ (pi : Equiv.Perm (Fin (d + 1))), q = upperCell d pi

                    A facet is entirely at time one exactly for an upper barycentric base facet.

                    The coordinates after the leading cone coordinate sum to 1 - w 0.

                    At the cone apex all tail coordinates vanish.

                    Normalize the tail barycentric coordinates away from the cone apex.

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                      Every recursive one-step cylinder chart is injective.

                      Every recursive cylinder cell has pairwise distinct ordered vertices.

                      Weighted pairing with the triangulated boundary simplex opposite the cone apex.

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                        The upper barycentric-subdivision boundary contribution.

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                          Recursive side-boundary contribution in positive dimension.

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