Bob Terrell
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 Jan21 comment Is there any “formula” that allows us make change of variables in surface integrals? I learned about the coarea formula in a lecture, and based on that I worked out the change of variables, so I don't have any references. There are some in the Wikipedia article that I haven't looked at. Dec8 awarded Caucus Oct23 answered Are there mathematical contexts where “finite” implicitly means “nonzero?” Oct8 answered Confused solving quasilinear PDE Sep6 awarded Yearling Aug18 awarded Informed May23 asked Is there a difference between “unity” and 1 in applied mathematics? Feb12 answered Vector Delta Function Identity Feb12 comment Vector Delta Function Identity The 1-dimensional version doesn't seem to work for $g(a)=-a$, since $\delta(-a) = \delta(a)$. Also the $n$-dimensional case needs a sum over roots too I think. Dec11 comment Norm of a matrix equals greatest eigenvalue Please add the word "symmetric" in the title. Nov3 answered A Neat Rotation Matrix Identity Sep25 answered Equivalence of integral and differential forms of transport equation Sep22 answered geometrical interpretation of cokernel Sep17 answered Is there any “formula” that allows us make change of variables in surface integrals? Sep17 answered Surface integral over an inconvenient surface Sep13 answered Transformation nonlinear PDE to system of ODE Sep13 answered Second order linear homogeneous ODE with constant coefficients and repeated roots. Why second solution needed? Sep6 awarded Yearling Aug16 awarded Revival Aug15 comment Why $\vec{r}$ is commonly use for vector equation? Though obviously false, the following explanation has been popular with my students: It is a verbal joke (which only works in English): since the vector gives your location from the origin, it tells you where you "are".