Siyuan Ren
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 Apr 9 awarded Notable Question Jul 25 awarded Teacher Jul 25 answered Why the determinant of a matrix with the sum of each row's elements equal 0 is 0? Jan 22 comment Why can a circle be described by an equation but not by a function? This answer makes me realize that the question isn't so simple as it seems. Dec 20 awarded Caucus Jul 2 awarded Curious Mar 20 awarded Popular Question Sep 10 comment A question about Killing vector and Riemann curvature tensor I've left the field of math and physics and am no longer able to decipher these symbols. Sorry about your first answer. But someone else who has the same problem may one day find you answer helpful. May 15 awarded Caucus Dec 29 asked Is it possible to further simplify the product of three exponentials $e^A e^B e^C$ when $[A,C]=kB$ (k is a scalar) Sep 14 awarded Commentator Sep 14 comment Complex analysis and powers of complex values Shouldn't the second one be $\pm 1$? Since complex power to fraction is multivalued. Sep 14 accepted Why is positivity of first entry sufficient for a matrix in $\mathrm{SO}(1,3)$ to be in $\mathrm{SO}^{+}(1,3)$? Sep 14 awarded Yearling Sep 14 awarded Editor Sep 14 revised Why is positivity of first entry sufficient for a matrix in $\mathrm{SO}(1,3)$ to be in $\mathrm{SO}^{+}(1,3)$? added 27 characters in body Sep 14 asked Why is positivity of first entry sufficient for a matrix in $\mathrm{SO}(1,3)$ to be in $\mathrm{SO}^{+}(1,3)$? Jun 20 comment What transforms under SU(2) as a matrix under SO(3)? I stated clearly in my question: what is the equivalent transformation in SU(2) of the rotation of a linear operator (matrix) instead of vector in $\mathbb{R}^3$? Jun 20 comment What transforms under SU(2) as a matrix under SO(3)? You are just re-expressing what I already know, that $\left( \boldsymbol{r}'\cdot\boldsymbol{\sigma} \right) = \boldsymbol{h} \left( \boldsymbol{r}\cdot\boldsymbol{\sigma} \right) \boldsymbol{h}^{-1}$. Jun 20 comment What transforms under SU(2) as a matrix under SO(3)? @QiaochuYuan: I didn't learn the concept of "pullback". Can you elaborate?