01
广义相对论与宇宙学
Relativity, Gravitation and Cosmology 全书中英切换笔记
Bilingual full-text notebook with figures and MathJax.
02
从偏折角到透镜会聚
从偏折角散度到透镜会聚的逐步推导
A readable derivation of the lensing divergence relation and Poisson equation.
03
透镜推导的矢量微积分背景
极坐标散度、二维散度定理与 delta 函数的配套解释
A companion note for polar divergence, the divergence theorem, and the two-dimensional delta function.
04
Lensing Jacobian
为什么雅可比矩阵由会聚和剪切组成，以及放大率为什么是行列式的倒数
Why the Jacobian is written with convergence and shear, and why magnification is the inverse determinant.
05
临界面密度与透镜 kappa
从临界面密度到 Jacobian 里的 convergence 的完整连接
How critical surface density becomes the convergence term in the lensing Jacobian.
06
时间延迟距离与 Fermat potential
从几何路径差和引力势延迟推导 time delay 公式，并配有薄透镜几何图
How geometrical and potential delays become the time-delay distance times a Fermat-potential difference.