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5
votes
Injectivity of an integral operator
Your operator $K$ is a Hilbert-Schmidt operator since its kernel belongs to $L^2$. As a result this is a compact operator whose spectrum contains a sequence of eigenvalues $\\{\lambda_k\not=0\\}$ with …
4
votes
Accepted
Improper integral $\int^\infty_0 e^{-a x^2} \cosh (b\sqrt{1+x^2})$
Let us give only an expansion in $a,b$. Calling $I(a,b)$ the integral, we get easily
$$
I(a,b)=\sum_{k\ge 0}\frac{b^{2k}}{(2k)!}\underbrace{e^{a}\int_0^{+\infty} e^{-a (x^2+1)}(1+x^2)^k dx}_{J_k(a)}.
…
2
votes
Accepted
When does an inverse PDE operator have a kernel (i.e. a fundamental solution?)
Following your assumptions, it seems that the mapping $L^{-1}$ sends linearly and continuously the smooth compactly supported functions into distributions and thus, from the Schwartz (Laurent) kernel …
2
votes
Boundedness of integral operators on spaces of continuous functions
Too long for a comment. Your requirement is too stringent and it is quite likely that to get continuity from $L^\infty$ into itself, it is indeed necessary to have
$$
\text{esssup}_x\int\vert k(x,y)\v …
1
vote
Well-definedness for a singular integral
Assuming the function $f$ of class $C^1$,
you find that, using Taylor's formula with integral remainder,
$$
f(t)-f(s)=(t-s) f_1(t,s),\quad \text{with $f_1$ continuous},$$
so that
$
(T_\alpha f)(t)= …