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Questions about the properties of vector spaces and linear transformations, including linear systems in general.
9
votes
Accepted
Efficiently computing $\prod_{i=1}^{n} A_i$
To be unambiguous about the order of multiplication, let $B(n) = A_1 A_2 \cdots A_n$. We have the D-finite recurrences
$B(n)_{r,1} = (\frac{n}{n-1})^k B(n-1)_{r,1} + n^k B(n-2)_{r,1}$
$B(n)_{r,2} = B …
5
votes
Accepted
Guess the next polynoms in the sequence (MO vs. AI :), count anticommuting $F_p$-matrices, P...
It's not entirely clear to me how much data your guesses are based on, so I present a table with calculated data and guessed polynomials based on that data and the assumption that $f(1) = f(-1) = 1$.
…
1
vote
Recurrence relation with two variables
The solutions look like a mess, so it's not too surprising that you always end up with one. If we follow Iosif Pinelis in dividing all by the last constraint by $\lambda$ and substituting $r = \frac{1 …
5
votes
Matrices over $\mathbb{F}_p$ that have nonzero determinant under any element permutation
$\det \begin{pmatrix} 1 \end{pmatrix} = 1$ works for any $p$.
$\det \begin{pmatrix} 0 & 1 \\ 1 & 1 \end{pmatrix} = -1$ similarly.
For $n=3$ we require $p \ge 5$. By exhaustion there's no solution for …
2
votes
Accepted
Inflection point calculation for cubic Bézier curve encounters division by zero
You're trying to solve $$(3a_xt^2 + 2b_xt + c_x)(6a_yt + 2b_y) - (6a_xt + 2b_x)(3a_yt^2 + 2b_yt + c_y) = 0$$
Expanded out, $$6(a_y b_x - a_x b_y) t^2 + 6(a_y c_x - a_x c_y)t + 2(b_y c_x - b_x c_y) = 0 …
2
votes
Non-singular matrix with restricted entries
Disclaimer: this is only a partial answer.
If $S = \{x, y\}$ (considered as variables), the determinant must be a polynomial with integer coefficients and constant coefficient 1. Therefore by Gauss's …
4
votes
Sum of divisors and LCM in determinants
This is only empirical observation, but I was requested to post it as an answer rather than merely a comment.
Define $b(n) = \frac{\det(A_n)}{n! \, \sigma(\operatorname{lcm}(1,\ldots,n))}$ for $n \ge …
3
votes
Vandermonde $V_n$ mod $n$
OP asked me to fill in the details of my comment, and in attempting to do so I realised that I claimed too much. However, a very similar argument proves a weaker result which is strong enough to suppo …