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Special functions, orthogonal polynomials, harmonic analysis, ordinary differential equations (ODE's), differential relations, calculus of variations, approximations, expansions, asymptotics.

4 votes

Why is the Laplacian ubiquitous?

The Laplacian is a second order differential operator which is both linear and invariant under any rigid body motion (rotations and translations). There is no simpler non-trivial operator with these …
Marc Chamberland's user avatar
1 vote

Nonvanishing of Jacobians implies global injectivity?

The answer is NO. Consider the two-dimensional example $F=(f,g)$ with $$ f(x,y) = \sqrt{2}e^{x/2}\cos(ye^{-x}) $$ $$ g(x,y) = \sqrt{2}e^{x/2}\sin(ye^{-x}) $$ The determinant of the Jacobian matrix is …
Marc Chamberland's user avatar
0 votes

Asymptotic estimates for the Exponential

This is a standard calculus question. Let $z(n) = (1−f(n))^{g(n)}$. Then $\log z(n) = g(n) \log( 1 - f(n))$. Assuming $f(n)\rightarrow 0$, one has $\log z(n)/( f(n)g(n) ) \rightarrow -1$. For your p …
Marc Chamberland's user avatar