querent

Spam yourself with math PhD qualifying-exam questions.

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UC Irvine Spring 2025, 3 Complex analysis, Cauchy–Riemann equations, harmonic functions, harmonic conjugates

Let Ω be an open set in ℂ, and let 𝑢(𝑥,𝑦),𝑣(𝑥,𝑦) be real-valued functions with continuous partial derivatives in Ω satisfying the Cauchy-Riemann equations. Assume also that

𝑢2+𝑣2≠0

on Ω. Prove that

is harmonic in Ω and find its harmonic conjugate on Ω if it exists.

UC Irvine Spring 2025, 4 Complex analysis, Chebyshev-type inequalities, polynomial growth, bounded polynomials

Let 𝑃(𝑧) be a polynomial of degree 𝑑 with complex coefficients such that

|𝑃(𝑥)|≤1

for all 𝑥∈[−1,1]. Show that

|𝑃(5)|≤10𝑑.
UC Irvine Spring 2025, 5 Complex analysis, contour integration, residues, real integrals

Use contour integration to show that for all integers 𝑛≥2,

∫0∞d𝑥1+𝑥𝑛=𝜋𝑛sin(𝜋/𝑛).
UC Irvine Spring 2025, 6 Complex analysis, Schwarz lemma, fixed points, self-maps of the disk

Suppose 𝑓:𝐷→𝐷 is a holomorphic function with two distinct fixed points 𝑎,𝑏∈𝐷, so

𝑓(𝑎)=𝑎,𝑓(𝑏)=𝑏,𝑎≠𝑏.

Prove that

𝑓(𝑧)=𝑧

for all 𝑧∈𝐷.

UC Irvine Spring 2025, 7 Complex analysis, conformal maps, slit plane, Riemann mapping

Find an explicit conformal map between

Ω=ℂ\((−∞,−1]∪[1,∞))

and the unit disk 𝐷.

UC Irvine Spring 2025, 8 Complex analysis, power series, natural boundary, continuous extension

Consider

𝑓(𝑧)=∑𝑛=0∞𝑧𝑛!𝑛!.

Show that 𝑓 is a bounded holomorphic function on the unit disk 𝐷 that admits a continuous extension to , but cannot be holomorphically extended to any neighborhood 𝐷(𝑝,𝜀) of any point .

UC Irvine Spring 2025, 9 Complex analysis, entire functions, interpolation, growth bounds

First, find an example of a pair of distinct entire functions 𝑓 and 𝑔 such that

𝑓(𝑛)=𝑔(𝑛)

for all 𝑛∈ℕ.

Show that it is impossible to find a distinct pair with this property if we further assume

|𝑓(𝑧)|+|𝑔(𝑧)|≤𝑒|𝑧|

for all 𝑧∈ℂ.

UC Irvine Spring 2026, 1 Complex analysis, holomorphic functions, antiderivatives, partial fractions

Prove or disprove that there exists a holomorphic function

𝐹:{𝑧∈ℂ:|𝑧|>3}→ℂ

such that

𝐹′(𝑧)=𝑧3+1(𝑧+1)(𝑧+2)−7𝑧−10𝑧2+1.
UC Irvine Spring 2026, 2 Complex analysis, holomorphic functions, nonvanishing functions, roots

Let 𝑓 be a holomorphic function on

𝔻={𝑧∈ℂ:|𝑧|<1}

such that 𝑓(0)=0 and 𝑓(𝑧)≠0 whenever 𝑧≠0. Let 𝑛∈ℕ. Prove that there exists a holomorphic function 𝑔 on 𝔻 such that

𝑔(𝑧)𝑛=𝑓(𝑧𝑛)

for every 𝑧∈𝔻.

UC Irvine Spring 2026, 3 Complex analysis, entire functions, growth bounds, lattice zeros

Find all entire functions 𝑓 such that

|𝑓(𝑧)|≤𝑒|𝑧|

for every 𝑧∈ℂ, and

𝑓(𝑚+∈)=0

for all 𝑚,𝑛∈ℕ.

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