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 2d comment Choosing between SOV/Green's functions/Laplace transform for solving PDE - Guideline for choosing the most appropriate method? Crossposted from physics.stackexchange.com/q/203713/2451 Aug 21 comment Can $S^4$ be the cotangent bundle of a manifold? Ups: Noticed crossposting: math.stackexchange.com/q/1402849/11127 Please don't crosspost. Instead ask for migration. Aug 21 comment Construct bivariate symmetric (polynomial) nonnegative functions (distributions) over the unit square with certain properties Crossposted to physics.stackexchange.com/q/201369/2451 Aug 20 answered Can $S^4$ be the cotangent bundle of a manifold? Aug 14 comment Number of independent components of a unitary matrix Hint: An complex $n\times n$ matrix contains $2n^2$ real d.o.f. Aug 10 comment Finding the closest function describing a “magnetic line” (given magnetic readings) Crossposted to physics.stackexchange.com/q/199434/2451 Aug 10 comment If the curl of some vector function = 0, Is it a must that this vector function is the gradient of some other scalar function? Would Mathematics be a better home for this question? Aug 7 comment How to show that $\int_{-\infty}^{\infty} \mathrm{d}^3 \textbf{k} \frac {e^{i \textbf{k x}}} {(2 \pi)^3} = \delta^3(x)$ in spherical coordinates? When considering the 3D Dirac delta distribution $\delta^3({\bf x})$ using coordinates, one should use a coordinate system that is defined in an open neighborhood of the support $\{{\bf 0}\}$ of the distribution. Spherical coordinates fail in that department. Aug 6 comment Question on symplectic geometry Crossposted from mathoverflow.net/q/213105/13917 Jul 31 comment Choice of order in the Leibniz rule is arbitrary? The assignment of positive orientations for the orientable manifolds $M$ and $\partial M$ in Stokes theorem $\int_M \!d_{L,R}\omega ~=~\int_{\partial M} \! \omega$ would have to be adjusted appropriately to make the Stokes formula work. We leave the details to the reader. Jul 30 answered Choice of order in the Leibniz rule is arbitrary? Jul 22 comment The Riemannian Curvature in a solid sphere ...where a solid sphere is technically called a ball $B^3$. Jul 21 comment Maximisation of the distance of particles in a periodic box Crossposted from physics.stackexchange.com/q/195000/2451 Jul 18 comment Second order PDE and its equivalent First order Representation Crossposted to physics.stackexchange.com/q/194631/2451 Jul 18 revised Derivative of solution of differential equation with respect to parameter Corrected solution and added simpler method. Jul 17 revised Derivative of solution of differential equation with respect to parameter Added explanation Jul 17 answered Derivative of solution of differential equation with respect to parameter Jul 15 revised What's going on with these identities involving $d$, $\mathcal L_X$, and $\iota_X$? Added explanation Jul 14 answered What's going on with these identities involving $d$, $\mathcal L_X$, and $\iota_X$? Jul 3 comment Fundamental Lemma of the Calculus of Variations with higher derivatives Related question on Phys.SE: physics.stackexchange.com/a/172361/2451