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Questions about the properties of vector spaces and linear transformations, including linear systems in general.
2
votes
fast way to calculate normal to set of vectors with $\pm$1 entries
There is a six-dimensional counterexample:
$(+1,+1,+1,+1,+1,+1)$
$(-1,-1,+1,+1,+1,+1)$
$(+1,+1,-1,-1,+1,+1)$
$(+1,+1,+1,-1,-1,+1)$
$(+1,-1,+1,-1,+1,-1)$
The normal to the linear span of these five …
1
vote
Accepted
Closest vertex in a 3D fcc lattice
Recall that the face-centred cubic lattice comprises all vectors in $\mathbb{Z}^3$ whose coordinate sum is even.
Let $(x, y, z) \in \mathbb{R}^3$. For each coordinate, define the discrepancy to be th …
1
vote
2
answers
460
views
'Positive-definite' matrices over finite fields
Let $X$ be an $n \times n$ invertible square matrix over some field $\mathbb{F}$, and let $Y = XX^T$ be the product of the matrix with its transpose.
When $\mathbb{F} = \mathbb{R}$, $Y$ is positive-d …
10
votes
Decide if a matrix is transposable
There are polynomial-time reductions from your problem to Graph Isomorphism and vice-versa.
As a quick definition, when I speak of 'subdividing' an edge, I mean to replace each edge $u, v$ with a pat …
4
votes
Unusual symmetries of the Cayley-Menger determinant for the volume of tetrahedra
The following comment in the question intrigued me:
In fact, it's possible to show that the linear symmetries of
$\mathbb{R}^6$ that preserve the Cayley-Menger determinant form the
Weyl group $D_6$, …