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 Dec 10 awarded Nice Answer Jun 25 awarded Yearling Apr 26 answered Construction of finite element differential forms based on deRham sequences Jan 18 answered reduced symplectic form Oct 19 awarded Yearling Jul 29 answered Example of symplectic and hamiltonian diffeomorphism on $S^2$ and $T^2$ Apr 7 answered integration of a laplacian Apr 7 comment Weakest condition for an integrable, almost-symplectic manifold? Do you mean Liouville's theorem (the Hamiltonian vector field preserves the symplectic form) or Liouville integrability (maximal set of first integrals in involution)? Apr 6 comment FEM on a Laplacian $H^{-1}$ is the dual space of $H^1$. This is actually even weaker than being in $L^2$ (a.k.a. $H^0$), since it's only a continuous functional when applied to weakly differentiable test functions. For example, consider the 1-D Dirac $\delta$-function, $\delta = \mathrm{H} '$, where $\mathrm{H}$ is the Heaviside step function. This is obviously not in $L^2$; however, it is in $H^{-1}$, since $(\delta, v) = (\mathrm{H}', v) = -(\mathrm{H}, v') \leq \lVert \mathrm{H} \rvert _{L^2} \lVert v \rVert _{H^1}$. This means that you can even make sense of the PDE $u'' = \delta$. Apr 6 answered FEM on a Laplacian Dec 23 revised $\ell^p$ version of singular values caught a mistake Dec 22 revised $\ell^p$ version of singular values added 179 characters in body Dec 22 revised Question about Banach's matchbox problem. added code; edited body Dec 22 answered $\ell^p$ version of singular values Dec 22 answered Question about Banach's matchbox problem. Oct 19 awarded Yearling Jun 18 answered Proving Hodge decomposition without using the theory of elliptic operators? May 28 awarded Enlightened May 28 awarded Nice Answer May 26 answered What are “variational crimes” and who coined the term?