# mathlib3documentation

linear_algebra.matrix.nondegenerate

# Matrices associated with non-degenerate bilinear forms #

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## Main definitions #

• matrix.nondegenerate A: the proposition that when interpreted as a bilinear form, the matrix A is nondegenerate.
def matrix.nondegenerate {m : Type u_1} {R : Type u_2} [fintype m] [comm_ring R] (M : m R) :
Prop

A matrix M is nondegenerate if for all v ≠ 0, there is a w ≠ 0 with w ⬝ M ⬝ v ≠ 0.

Equations
theorem matrix.nondegenerate.eq_zero_of_ortho {m : Type u_1} {R : Type u_2} [fintype m] [comm_ring R] {M : m R} (hM : M.nondegenerate) {v : m R} (hv : (w : m R), (M.mul_vec w) = 0) :
v = 0

If M is nondegenerate and w ⬝ M ⬝ v = 0 for all w, then v = 0.

theorem matrix.nondegenerate.exists_not_ortho_of_ne_zero {m : Type u_1} {R : Type u_2} [fintype m] [comm_ring R] {M : m R} (hM : M.nondegenerate) {v : m R} (hv : v 0) :
(w : m R), (M.mul_vec w) 0

If M is nondegenerate and v ≠ 0, then there is some w such that w ⬝ M ⬝ v ≠ 0.

theorem matrix.nondegenerate_of_det_ne_zero {m : Type u_1} {A : Type u_3} [fintype m] [comm_ring A] [is_domain A] [decidable_eq m] {M : m A} (hM : M.det 0) :

If M has a nonzero determinant, then M as a bilinear form on n → A is nondegenerate.

See also bilin_form.nondegenerate_of_det_ne_zero' and bilin_form.nondegenerate_of_det_ne_zero.

theorem matrix.eq_zero_of_vec_mul_eq_zero {m : Type u_1} {A : Type u_3} [fintype m] [comm_ring A] [is_domain A] [decidable_eq m] {M : m A} (hM : M.det 0) {v : m A} (hv : = 0) :
v = 0
theorem matrix.eq_zero_of_mul_vec_eq_zero {m : Type u_1} {A : Type u_3} [fintype m] [comm_ring A] [is_domain A] [decidable_eq m] {M : m A} (hM : M.det 0) {v : m A} (hv : M.mul_vec v = 0) :
v = 0