Recent notes

Water waves, mathematics & computation

Bing-Hai Lei’s notes on theoretical fluid mechanics, numerical methods, and the mathematics behind them—derivations, reading trails, and reusable calculations.

Fourier Multipliers as Operators

Fourier Multipliers as Operators Fourier analysis is especially useful for linear, translation-invariant operators. In physical space, such an operator may involve derivatives…

Mathematics
Kelvin WedgeReading NoteIn Progress

What does $x^{\prime}$ mean in a Green’s function? — a linear algebra and operator view

In a Green's function \(G(x,x')\), the primed variable \(x'\) marks the source point — the location of a unit impulse — while \(x\) is the field point where the response is…

Fluid Mechanics

人应该怎样度过一生 一

浓雾氤氲的森林,分不清是清晨还是黄昏,天边应该是有丝丝破碎的晨曦亦或是夕阳,还未走进你眼眸,便融化进了昏霭,染成一片模糊的光晕。你的思绪也仿若虚无之地,白茫茫一片,犹豫,抬起脚,犹豫,犹豫,犹豫,向前?向后?是追忆还是邂逅迷茫?

随想 Reflections
Kelvin WedgeReading NoteIn Progress

From the Spectral Dirichlet-Neumann Symbol to the Physical-Space Operator Identity

We show how the spectral relation ∑ Formula implies the physical-space operator identity ∑ Formula, by inverse Fourier transform and the commutation of \(\partial_z\) with the hori…

Fluid Mechanics
Kelvin WedgeDerivationNegative Result

Hankel Diagonalization of the Radial Bessel Operator

The math is sound. The method is not. We show that the order- \(n\) Hankel transform in \(r\) diagonalizes the Bessel-type radial operator \(\mathscr{L}_n\), mapping the PDE…

Mathematics
12314