<aside> 🧸 本文简单说明了如何用轮椅跑路。 QFT
</aside>
Mark Srednick: Quantum Field theory https://web.physics.ucsb.edu/~mark/ms-qft-DRAFT.pdf
Peskin Schroeder: Introduction to QFT
Peskin, An Introduction to Quantum Field Theory.pdf
Steven Weinberg: Quantum theory of Fields Vol I II
Weinberg - 1995 - The Quantum Theory of Fields Volume 1 Foundations.pdf
Altman, Simons: Condensed matter Field theory
Altl and er - Condensed Matter Field Theory, Second Edition.pdf
position space(configuration space)
$$ \int[dg(t)] $$
phase space
$$ \int [dg(t)][dp(t)] $$
→ Integration in functional space, such as
$$ C=\{x(t)\mid x(t_a)=a,x(t_b)=b\} $$
<aside>
变分法基本引理
借助另一个东西描述此函数：
弱导数
取$[a,b]$上的任意阶可微函数$\eta(x)$，若$\eta(a)=\eta(b)=0$
$$ \forall \eta(x)\in\Omega_0^\infty[a,b],\int_a^b f(x)\eta(x)dx=0 $$
则零函数。
$\Omega_0^\infty[a,b]$ 是一个线性空间。
证明：保号性
</aside>