Jean-Claude Arbaut
Reputation
10,605
89/100 score
 2d awarded Nice Answer Apr 30 comment If $au + bv + cw = 0$ with $a+b + c = 0$ then $u,v,w$ are collinear Ok, however $a+b=0$ with $a\neq 0$ and $b\neq 0$, and $c=0$ won't help much: in that case, $u,v$ are collinear, and you know nothing about $w$. However, you know for sure $u,v,w$ are coplanar. Apr 29 reviewed No Action Needed Is there a simpler function with this shape? Apr 29 reviewed Looks OK Is there any integral for the Golden Ratio? Apr 29 reviewed Reopen Lebesgue measure-preserving differentiable function Apr 24 reviewed Looks OK Is there convergence in this sequence? Apr 24 reviewed No Action Needed Probability of a set of random integers containing number in specific range Apr 22 reviewed Looks OK How to calculate this integral using dominated convergence theorem? Apr 22 reviewed Close Integrating division Apr 22 reviewed Leave Open What was the first bit of mathematics that made you realize that math is beautiful? (For children's book) Apr 22 reviewed Leave Open If $K\cap\Bbb Q^{\text{cycl}}=\Bbb Q(\zeta_m)$ and $K/\Bbb Q$ Galois, then $\text{Gal}(K(\zeta_n)/K)\cong\text{Gal}(\Bbb Q(\zeta_n)/\Bbb Q(\zeta_m))$ Apr 22 reviewed Close Color the edges of $K_6$ red or blue. Prove that there is a cycle of length 4 with monochromatic edges. Apr 22 reviewed Reopen Diffeomorphism group of product manifold Apr 22 comment Complexity of Gaussian Process algorithms is $\mathcal{O}(n^3)$ EHHH, Gaussian elimination is an $O(n^3)$ algorithm, however it does not make use of matrix product. To solve a linear system $Au=v$, you may first inverse the matrix (also with Gaussian elimination, but in a slightly different way as you solve $n$ systems instead of a single one, still in $O(n^3)$) and compute afterwards $u=A^{-1}v$, but then this last matrix-vector product is $O(n^2)$. Apr 22 comment Write $π = (3, 2, 5)(2, 5, 4)$ in “table” notation? Chris, you really have to tell which convention you assume for the product of permutations, as both are used (left-to-right and right-to-left). JMoravitz and probablyme answers are both correct. Apr 21 reviewed Reopen Generalisation of the sum operator for the divergent geometric series Apr 20 reviewed Looks OK Distance between points in a square Apr 20 reviewed Approve Implementation of Jacobi theta functions in Matlab Apr 20 reviewed Approve Exponentiation on the natural numbers. Prove the identities $n^{(m+k)}=n^m \cdot n^k$ and $n^{(m \cdot k)}=(n^m)^k$. Apr 20 reviewed No Action Needed (partial) Derivative of norm of vector with respect to norm of vector