数学公式备忘

2024-03-17
4 min read

Sympy 求解是不错的选择

微积分

导数

参考:考研数学公式大全 / Wiki /

\[\begin{aligned} (\operatorname{tg} x)^{\prime} & =\sec ^2 x & (\arcsin x)^{\prime} & =\frac{1}{\sqrt{1-x^2}} \\ (\operatorname{ctg} x)^{\prime} & =-\csc ^2 x & (\arccos x)^{\prime} & =-\frac{1}{\sqrt{1-x^2}} \\ (\sec x)^{\prime} & =\sec x \cdot \operatorname{tg} x & (\operatorname{arctg} x)^{\prime} & =\frac{1}{1+x^2} \\ (\csc x)^{\prime} & =-\csc x \cdot \operatorname{ctg} x & (\operatorname{arcctg} x)^{\prime} & =-\frac{1}{1+x^2} \\ \left(a^x\right)^{\prime} & =a^x \ln a & & \end{aligned} \]

运算法则(导数表):

\[\begin{aligned} \frac{\mathrm{d}}{\mathrm{d} x}(f+g) & =\frac{\mathrm{d} f}{\mathrm{~d} x}+\frac{\mathrm{d} g}{\mathrm{~d} x} & \frac{\mathrm{d}}{\mathrm{d} x}[f(g(x))] & =\frac{\mathrm{d} f}{\mathrm{~d} g} \cdot \frac{\mathrm{d} g}{\mathrm{~d} x}=f^{\prime}(g(x)) \cdot g^{\prime}(x) \\ \frac{\mathrm{d}}{\mathrm{d} x}(c \cdot f) & =c \cdot \frac{\mathrm{d} f}{\mathrm{~d} x} & \frac{\mathrm{d}^n}{\mathrm{~d} x^n} f(x) g(x) & =\sum_{i=0}^n\left(\begin{array}{c} n \\ i \end{array}\right) f^{(n-i)}(x) g^{(i)}(x) \\ \frac{\mathrm{d}}{\mathrm{d} x}(f \cdot g) & =f \cdot \frac{\mathrm{d} g}{\mathrm{~d} x}+g \cdot \frac{\mathrm{d} f}{\mathrm{~d} x} & \frac{\mathrm{d}}{\mathrm{d} x}\left(\frac{1}{f}\right) & =-\frac{f^{\prime}}{f^2} \\ \frac{\mathrm{d}}{\mathrm{d} x}\left(\frac{f}{g}\right) & =\frac{-f \cdot \frac{\mathrm{d} g}{d x}+g \cdot \frac{\mathrm{d} f}{\mathrm{~d} x}}{g^2} & & \end{aligned} \]

积分

参考:常用积分表 / 积分表 /

\[\begin{array}{ll} \int k \mathrm{~d} x=k x+C(k \text { 是常数 }), & \int \frac{\mathrm{d} x}{\sqrt{1-x^2}}=\arcsin x+C, \\ \int x^{\prime \prime} \mathrm{d} x=\frac{x^{\mu+1}}{\mu+1}+C(\mu \neq-1), & \int a^x \mathrm{~d} x=\frac{a^x}{\ln a}+C, \\ \int \frac{\mathrm{d} x}{x}=\ln |x|+C, & \int \cos x \mathrm{~d} x=\sin x+C, \\ \int \frac{\mathrm{d} x}{1+x^2}=\arctan x+C, & \int \sin x \mathrm{~d} x=-\cos x+C, \end{array} \]

运算法则

\[\begin{aligned} \int c \cdot f(x) \mathrm{d} x & =c \cdot \int f(x) \mathrm{d} x \\ \int(f(x) \pm g(x)) \mathrm{d} x & =\int f(x) \mathrm{d} x \pm \int g(x) \mathrm{d} x \\ \int u d v & =u v-\int v d u \end{aligned} \]

泰勒级数

\[f(a)+\frac{f^{\prime}(a)}{1 !}(x-a)+\frac{f^{\prime \prime}(a)}{2 !}(x-a)^2+\frac{f^{\prime \prime \prime}(a)}{3 !}(x-a)^3+\cdots=\sum_{n=0}^{\infty} \frac{f^{(n)}(a)}{n !}(x-a)^n \]

参考:泰勒公式 / 1 / Wiki /

\[\begin{aligned} \ln (1+x) & =\sum_{k=1}^{\infty}(-1)^{k+1} \frac{x^k}{k}(-1 \lt x \leq 1) & \ln (1-x) & =-\sum_{k=1}^{\infty} \frac{x^k}{k}(-1 \leq x \lt 1) \\ \frac{1}{1-x} & =\sum_{n=0}^{\infty} x^n & \frac{1}{1+x} & =\sum_{n=0}^{\infty}(-1)^n x^n \\ e^x & =\sum_{k=0}^{\infty} \frac{x^k}{k !} & \sin x & =\sum_{n=0}^{\infty}(-1)^n \frac{x^{2 n+1}}{(2 n+1) !} \end{aligned} \]

复变函数与积分变换

拉普拉斯变换

参考:Wiki / 2 /

\[\begin{gathered}\mathscr{L}[f(t)]=F(s)=\int_0^{\infty} f(t) \mathrm{e}^{-t} \mathrm{~d} t \\ \mathscr{L}^{-1}[F(s)]=f(t)=\frac{1}{2 \pi \mathrm{j}} \int_{\sigma-\mathrm{j} \infty}^{\sigma+\mathrm{j} \infty} F(s) \mathrm{e}^{s t} \mathrm{~d} s\end{gathered} \]

运算法则

\[\begin{array}{|c|c|} \hline \text { Time domain } & s \text { domain } \\ \hline a f(t)+b g(t) & a F(s)+b G(s) \\ \hline t f(t) & -F^{\prime}(s) \\ \hline t^n f(t) & (-1)^n F^{(n)}(s) \\ \hline f^{\prime}(t) & s F(s)-f\left(0^{-}\right) \\ \hline f^{\prime \prime}(t) & s^2 F(s)-s f\left(0^{-}\right)-f^{\prime}\left(0^{-}\right) \\ \hline f^{(n)}(t) & s^n F(s)-\sum_{k=1}^n s^{n-k} f^{(k-1)}\left(0^{-}\right) \\ \hline \frac{1}{t} f(t) & \int_s^{\infty} F(\sigma) d \sigma \\ \hline \int_0^t f(\tau) d \tau=(u * f)(t) & \frac{1}{s} F(s) \\ \hline e^{a t} f(t) & F(s-a) \\ \hline f(t-a) u(t-a) & e^{-a s} F(s) \\ \hline f(t) u(t-a) & e^{-a s} \mathcal{L}\{f(t+a)\} \\ \hline f(a t) & \frac{1}{a} F\left(\frac{s}{a}\right) \\ \hline f(t) g(t) & \frac{1}{2 \pi i} \lim _{T \rightarrow \infty} \int_{c-i T}^{c+i T} F(\sigma) G(s-\sigma) d \sigma \\ \hline(f * g)(t)=\int_0^t f(\tau) g(t-\tau) d \tau & F(s) \cdot G(s) \\ \hline(f * g)(t)=\int_0^T f(\tau) g(t-\tau) d \tau & F(s) \cdot G(s) \\ \hline f^*(t) & F^*\left(s^*\right) \\ \hline(f \star g)(t)=\int_0^{\infty} f(\tau)^* g(t+\tau) d \tau & F^*\left(-s^*\right) \cdot G(s) \\ \hline f(t) & \frac{1}{1-e^{-T s}} \int_0^T e^{-s t} f(t) d t \\ \hline \begin{array}{l} f_P(t)=\sum_{n=0}^{\infty} f(t-T n) \\ f_P(t)=\sum_{n=0}^{\infty}(-1)^n f(t-T n) \end{array} & \begin{array}{l} F_P(s)=\frac{1}{1-e^{-T s}} F(s) \\ F_P(s)=\frac{1}{1+e^{-T s}} F(s) \end{array} \\ \hline \end{array} \]

常见变换

\[\begin{array}{|c|c|c|} \hline \begin{array}{c} \text { Time domain } \\ f(t)=\mathcal{L}^{-1}\{F(s)\} \end{array} & \begin{array}{l} \text { Laplace s-domain } \\ F(s)=\mathcal{L}\{f(t)\} \end{array} & \begin{array}{l} \text { Region of } \\ \text { convergence } \end{array} \\ \hline \delta(t) & 1 & \text { all } s \\ \hline \delta(t-\tau) & e^{-\tau s} & \\ \hline u(t) & \frac{1}{s} & \operatorname{Re}(s)>0 \\ \hline u(t-\tau) & \frac{1}{s} e^{-\tau s} & \operatorname{Re}(s)>0 \\ \hline f(t-\tau) u(t-\tau) & e^{-s \tau} \mathcal{L}\{f(t)\} & \\ \hline u(t)-u(t-\tau) & \frac{1}{s}\left(1-e^{-\tau s}\right) & \operatorname{Re}(s)>0 \\ \hline t \cdot u(t) & \frac{1}{s^2} & \operatorname{Re}(s)>0 \\ \hline t^n \cdot u(t) & \frac{n !}{s^{n+1}} & \begin{array}{c} \operatorname{Re}(s)>0 \\ (n>-1) \end{array} \\ \hline t^q \cdot u(t) & \frac{\Gamma(q+1)}{s^{q+1}} & \begin{array}{c} \operatorname{Re}(s)>0 \\ \operatorname{Re}(q)>-1 \end{array} \\ \hline \sqrt[n]{t} \cdot u(t) & \frac{1}{s^{\frac{1}{n}+1}} \Gamma\left(\frac{1}{n}+1\right) & \operatorname{Re}(s)>0 \\ \hline t^n e^{-\alpha t} \cdot u(t) & \frac{n !}{(s+\alpha)^{n+1}} & \operatorname{Re}(s)>-\alpha \\ \hline(t-\tau)^n e^{-\alpha(t-\tau)} \cdot u(t-\tau) & \frac{n ! \cdot e^{-\tau s}}{(s+\alpha)^{n+1}} & \operatorname{Re}(s)>-\alpha \\ \hline e^{-\alpha t} \cdot u(t) & \frac{1}{s+\alpha} & \operatorname{Re}(s)>-\alpha \\ \hline e^{-\alpha|t|} & \frac{2 \alpha}{\alpha^2-s^2} & -\alpha<\operatorname{Re}(s)<\alpha \\ \hline\left(1-e^{-\alpha t}\right) \cdot u(t) & \frac{\alpha}{s(s+\alpha)} & \operatorname{Re}(s)>0 \\ \hline \sin (\omega t) \cdot u(t) & \frac{\omega}{s^2+\omega^2} & \operatorname{Re}(s)>0 \\ \hline \cos (\omega t) \cdot u(t) & \frac{s}{s^2+\omega^2} & \operatorname{Re}(s)>0 \\ \hline \sinh (\alpha t) \cdot u(t) & \frac{\alpha}{s^2-\alpha^2} & \operatorname{Re}(s)>|\alpha| \\ \hline \cosh (\alpha t) \cdot u(t) & \frac{s}{s^2-\alpha^2} & \operatorname{Re}(s)>|\alpha| \\ \hline e^{-\alpha t} \sin (\omega t) \cdot u(t) & \frac{\omega}{(s+\alpha)^2+\omega^2} & \operatorname{Re}(s)>-\alpha \\ \hline e^{-\alpha t} \cos (\omega t) \cdot u(t) & \frac{s+\alpha}{(s+\alpha)^2+\omega^2} & \operatorname{Re}(s)>-\alpha \\ \hline \ln (t) \cdot u(t) & -\frac{1}{s}[\ln (s)+\gamma] & \operatorname{Re}(s)>0 \\ \hline J_n(\omega t) \cdot u(t) & \frac{\left(\sqrt{s^2+\omega^2}-s\right)^n}{\omega^n \sqrt{s^2+\omega^2}} & \begin{array}{c} \operatorname{Re}(s)>0 \\ (n>-1) \end{array} \\ \hline \operatorname{erf}(t) \cdot u(t) & \frac{1}{s} e^{(1 / 4) s^2}\left(1-\operatorname{erf} \frac{s}{2}\right) & \operatorname{Re}(s)>0 \\ \hline \end{array} \]

拉氏变换与积分

参考 / 3,利用拉氏变换定义可证明如下公式。只有反常积分存在且收敛才可套用如下公式:

\[\begin{aligned} &\int_0^{+\infty} f(t) \mathrm{d} t=F(0)\\ &\int_0^{+\infty} t f(t) \mathrm{d} t=-F^{\prime}(0)\\ &\int_0^{+\infty} \frac{f(t)}{t} \mathrm{~d} t=\int_0^{\infty} F(s) \mathrm{d} s \end{aligned} \]

线代&矩阵

参考:线性代数公式定理一览表 /

行列式

代数余子式展开(\(A_{i j}=(-1)^{i+j} M_{i j}\)):

\[\begin{aligned} &D=a_{i 1} A_{i 1}+a_{i 2} A_{i 2}+\cdots+a_{i n} A_{i n}=\sum_{k=1}^n a_{i k} A_{i k} \quad(i=1,2, \ldots, n)\\ &D=a_{1 j} A_{1 j}+a_{2 j} A_{2 j}+\cdots+a_{n j} A_{n j}=\sum_{k=1}^n a_{k j} A_{k j} \quad(j=1,2, \ldots, n) \end{aligned} \]

范德蒙德

\[D_n=\left|\begin{array}{cccc} 1 & 1 & \ldots & 1 \\ x_1 & x_2 & \ldots & x_n \\ x_1^2 & x_2^2 & \ldots & x_n^2 \\ \vdots & \vdots & & \vdots \\ x_1^{n-1} & x_2^{n-1} & \ldots & x_n^{n-1} \end{array}\right|=\prod_{1 \leq i \lt j \leq n}\left(x_j-x_i\right) \]

矩阵转置&逆&正交

转置

  1. \((\lambda A)^T=\lambda A^T\)
  2. \((A \pm B)^T=A^T \pm B^T\)
  3. \((A B)^T=B^T A^T\)
  4. \(A\)\(n\) 阶方阵, 则 \(\left|A^T\right|=|A|\)
  5. \(\left(A^T\right)^T=A\)

  1. \(\lambda\) 是非零实数时, \(\lambda A\) 也可逆, 且 \((\lambda A)^{-1}=\frac{1}{\lambda} A^{-1}\)
  2. \(A B\) 可逆, 且 \((A B)^{-1}=B^{-1} A^{-1}\)
  3. \(A^T\) 可逆, 且 \(\left(A^T\right)^{-1}=\left(A^{-1}\right)^T\)
  4. \(A^{-1}\) 可逆, 且 \(\left(A^{-1}\right)^{-1}=A,\left|A^{-1}\right|=\frac{1}{|A|}\)
  5. \(A^*\) 可逆, 且 \(\left(A^*\right)^{-1}=\left(A^{-1}\right)^*=\frac{A}{|A|}, A^*=|A| A^{-1},\left|A^*\right|=|A|^{n-1}\)

已知 \(A\) 为正交矩阵则

  1. \(A^{-1}=A^T\) 也是正交阵;
  2. \(|A|= \pm 1\)
  3. \(B\) 也是正交阵, 则 \(A B\) 也是正交阵;
  4. \(A\) 的行(列)向量组构成 \(R^n\) 的一个标准正交基.

LaTeX

\(\LaTeX\)$\LaTeX$)示例,更多细节可以参考第三章

希腊字符

LaTex \(\LaTeX\) LaTex \(\LaTeX\) LaTex \(\LaTeX\) LaTex \(\LaTeX\)
\alpha \(\alpha\) \nu \(\nu\) \digamma \(\digamma\) \Pi \(\Pi\)
\beta \(\beta\) \kappa \(\kappa\) \varkappa \(\varkappa\) \Psi \(\Psi\)
\gamma \(\gamma\) \lambda \(\lambda\) \varpi \(\varpi\) \varrho \(\varrho\)
\delta \(\delta\) \mu \(\mu\) \varsigma \(\varsigma\) \Sigma \(\Sigma\)
\epsilon \(\epsilon\) \zeta \(\zeta\) \eth \(\eth\) \phi \(\phi\)
\eta \(\eta\) \theta \(\theta\) \upsilon \(\upsilon\) \varphi \(\varphi\)
\iota \(\iota\) \xi \(\xi\) \chi \(\chi\) \psi \(\psi\)
\pi \(\pi\) \rho \(\rho\) \omega \(\omega\) \vartheta \(\vartheta\)
\sigma \(\sigma\) \tau \(\tau\) \Omega \(\Omega\) \hbar \(\hbar\)
\Gamma \(\Gamma\) \Delta \(\Delta\) \varepsilon \(\varepsilon\) \Upsilon \(\Upsilon\)
\Lambda \(\Lambda\) \Phi \(\Phi\) \Xi \(\Xi\) \Theta \(\Theta\)

其他符号

LaTex \(\LaTeX\) LaTex \(\LaTeX\) LaTex \(\LaTeX\) LaTex \(\LaTeX\)
\partial \infty \(\infty\) \nrightarrow \(\nrightarrow\) \mapsto \(\mapsto\)
\wedge \vee \(\vee\) \geq \(\geq\) \leq \(\leq\)
\neg \(\neg\) \pm \(\pm\) \equiv \(\equiv\) \sim \(\sim\)
\bot \(\bot\) \top \gg \(\gg\) \ll \(\ll\)
\nabla \(\nabla\) \varnothing \subset \subseteq \(\subseteq\)
\angle \(\angle\) \measuredangle \(\measuredangle\) \in \notin \(\notin\)
\surd \(\surd\) \forall \(\forall\) \mid \(\mid\) \propto \(\propto\)
\exists \(\exists\) \nexists \(\nexists\) \perp \(\perp\)
\hookrightarrow \Rightarrow \vartriangle \(\vartriangle\)
\int \(\int\) \iint \(\iint\) \bigcup \(\bigcup\)
\iiint \(\iiint\) \parallel \(\parallel\) \bigcap \(\bigcap\) a a\ b \(a a\ b\)
\prod \(\prod\) \sum \(\sum\) \simeq \(\simeq\) a\quad b \(a\quad b\)
\rightarrow \(\rightarrow\) \Leftrightarrow \iff \(\iff\) a\qquad b \(a\qquad b\)

数学标记

LaTex \(\LaTeX\) 英文读法 LaTex \(\LaTeX\) 英文读法
x' / x^{\prime} \(x^{\prime}\) \(x\) prime x_i \(x_i\) \(x\) subscript \(\mathrm{i}, x\) sub \(\mathrm{i}\)
x'' \(x^{\prime \prime}\) \(x\) double prime x^i \(x^i\) \(x\) to the \(\mathrm{n}, x\) to the nth
\overrightarrow{AB} \(\overrightarrow{A B}\) vec pointing from \(A\) to \(B\) \ddot{x} \(\ddot{x}\) \(x\) double dot
\underline{x} \(\underline{x}\) \(x\) underline x^* \(x^*\) \(x\) star, \(x\) super asterisk
\hat{x} \(\hat{x}\) \(x\) hat x\dagger \(x \dagger\) \(x\) dagger
\bar{x} \(\bar{x}\) \(x\) bar x\ddagger \(x \ddagger\) \(x\) double dagger
\dot{x} \(\dot{x}\) \(x\) dot {\color{red}x} \({\color{red}x}\) red \({\color{red}x}\)
\tilde{x} \(\tilde{x}\) \(x\) tilde

字母样式

Latex \(\LaTeX\) 说明
{AaBbCc} \({AaBbCc}\) 斜体, 大部分数学符号、表达式
\mathrm {AaBbCc} \(\mathrm {AaBbCc}\) 正体, 公式中的单位或文字
\mathbf{AaBbCc} \(\mathbf{AaBbCc}\) 粗体, 向量、矩阵
\boldsymbol {AaBbCc} \(\boldsymbol {AaBbCc}\) 粗体、斜体, 向量、矩阵
\mathtt {AaBbCc} \(\mathtt {AaBbCc}\) 等宽字体, 常用于代码
\mathcal {AaBbCc} \(\mathcal{A B C D E F}\) 花体, 用于表示数学中的集合、代数结构、算子
\mathbb {AaBbCc} \(\mathbb {AaBbCc}\) 黑板粗体 (blackboard bold), 常用来表达各种集合
\text {Aa Bb Cc} \(\text {Aa Bb Cc}\) 用来写公式中的文字
\mathrm{d}x \(\mathrm{d}x\) ISO 规定导数符号 \(\mathrm{d}\) 为正体
\operatorname{T} \(\operatorname{T}\) 运算符

  1. Almendros, Ines N. Rodriguez . “Table of Integrals, Series, and Products.” (2009). ↩︎

  2. 郑君里, 应启珩, and 杨为理. 信号与系统.上册.3版. 高等教育出版社, 2011. ↩︎

  3. 李叶舟, and 刘文君. 复变函数及其应用. 北京邮电大学出版社, 2020. ↩︎