# Bases in normed affine spaces. #

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This file contains results about bases in normed affine spaces.

## Main definitions: #

• continuous_barycentric_coord
• is_open_map_barycentric_coord
• affine_basis.interior_convex_hull
• exists_subset_affine_independent_span_eq_top_of_open
• interior_convex_hull_nonempty_iff_affine_span_eq_top
theorem is_open_map_barycentric_coord {ι : Type u_1} {𝕜 : Type u_2} {E : Type u_3} {P : Type u_4} [ E] [metric_space P] [ P] [nontrivial ι] (b : 𝕜 P) (i : ι) :
@[continuity]
theorem continuous_barycentric_coord {ι : Type u_1} {𝕜 : Type u_2} {E : Type u_3} {P : Type u_4} [ E] [metric_space P] [ P] [ E] (b : 𝕜 P) (i : ι) :
theorem smooth_barycentric_coord {ι : Type u_1} {𝕜 : Type u_2} {E : Type u_3} [ E] [ E] (b : 𝕜 E) (i : ι) :
(b.coord i)
theorem affine_basis.interior_convex_hull {ι : Type u_1} {E : Type u_2} [finite ι] [ E] (b : E) :
interior ( (set.range b)) = {x : E | (i : ι), 0 < (b.coord i) x}

Given a finite-dimensional normed real vector space, the interior of the convex hull of an affine basis is the set of points whose barycentric coordinates are strictly positive with respect to this basis.

TODO Restate this result for affine spaces (instead of vector spaces) once the definition of convexity is generalised to this setting.

theorem is_open.exists_between_affine_independent_span_eq_top {V : Type u_1} {P : Type u_2} [ V] [metric_space P] [ P] {s u : set P} (hu : is_open u) (hsu : s u) (hne : s.nonempty) (h : coe) :
(t : set P), s t t u

Given a set s of affine-independent points belonging to an open set u, we may extend s to an affine basis, all of whose elements belong to u.

theorem is_open.exists_subset_affine_independent_span_eq_top {V : Type u_1} {P : Type u_2} [ V] [metric_space P] [ P] {u : set P} (hu : is_open u) (hne : u.nonempty) :
(s : set P) (H : s u),
theorem is_open.affine_span_eq_top {V : Type u_1} {P : Type u_2} [ V] [metric_space P] [ P] {u : set P} (hu : is_open u) (hne : u.nonempty) :

The affine span of a nonempty open set is ⊤.

theorem affine_span_eq_top_of_nonempty_interior {V : Type u_1} [ V] {s : set V} (hs : (interior ( s)).nonempty) :
theorem affine_basis.centroid_mem_interior_convex_hull {V : Type u_1} [ V] {ι : Type u_2} [fintype ι] (b : V) :
theorem convex.interior_nonempty_iff_affine_span_eq_top {V : Type u_1} [ V] {s : set V} (hs : s) :