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Spectrum, resolvent, numerical range, functional calculus, operator semigroups. Special classes of operators: compact, Fredholm, dissipative, differential, integral, pseudodifferential, etc.
5
votes
Eigenfunctions and eigenvalues of an operator defined by a certain integral
The inverse operator is $L^{-1} = 1/2 \cdot (x-1)^{-1} d^2/dx^2 - 1/2 \cdot (x-1)^{-2} d/dx$. Its eigenfunctions are derivatives of Airy functions, $Ai^{\prime } ((2\lambda )^{1/3} (x-1))$, $Bi^{\prim …
4
votes
The Quotient exponential operator
The exponentiated operator shifts $f$ by one unit in $x$, i.e.,
$$
\frac{1}{e^{d/dx} (f(x))} = \frac{1}{f(x+1)}
$$
It's not quite clear what is desired by "getting rid of the denominator" - the result …
3
votes
Accepted
Is the evolution family self-adjoint?
No, $U(t,s)$ is, in general, not self-adjoint. If we, for ease of formulation, denote the parameters $t,s$ as "times", then $U(t,s)$ is given by the time-ordered exponential
$$
U(t,s) = T\exp \left( \ …
2
votes
Explicit form of S-matrix on the line
Paraphrasing L.I.Schiff, "Quantum Mechanics", the $S$-matrix $S=\langle \beta | \alpha^{+} \rangle $ is the amplitude of the final asymptotic state $\beta $ contained in what became of an initial asym …
1
vote
The operator of exponential derivative applied in quotients
You haven't really defined $(d/dy)^{-1} $, but let's pick, for instance, $(d/dy)^{-1} f(y) = \int_{0}^{y} dy' f(y')$. Then, your two expressions for $H(y)$ in general are not equal. A simple counterex …
1
vote
A question regarding Hermite polynomials and exponential operators $\exp[e^{x^2/2}p(\frac{d}...
You can of course write
$$
k(x,t) = \exp \left[ e^{-t^2 /2} p\left( -\frac{d}{dt} \right) e^{t^2 /2} \right] \delta (x-t)
$$
Not clear whether that affords you any sort of simplification you may be po …