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

5 votes
1 answer
314 views

Implicit function theorem with singularities of any order

Let $\mathcal{U}\subset \mathbb{R}\times \mathbb{C}$ a neighborhood of $(0,0)$, and $f:\mathcal{U}\to \mathbb{C}$ differentiable in the first variable and holomorphic in the second variable, with $f(0 …
Lorenzo Q's user avatar
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1 vote
Accepted

Implicit function theorem with singularities of any order

Rouché's theorem provides a simple solution. Let $f_1(x,z)=z^k+x^h$ and $f_2(x,z)=h.o.t.$. For each $x$, the functions $f_1$ and $f_2$ are holomorphic in $z$. We know $f_2(x,z)=o(z^k)+o(x^h)$, so ther …
Lorenzo Q's user avatar
  • 211