[R] 用 `expression()` 在图中展示数学公式

?plotmath

[R: Mathematical Annotation in R (mit.edu)](https://web.mit.edu/~r/current/arch/i386_linux26/lib/R/library/grDevices/html/plotmath.html#:~:text=Mathematical Annotation in R Description If the text,output will be formatted according to TeX-like rules.)

1 Basic operators

Syntax	Meaning
%*%	$\times$
%/%	$\div$
%+-%	$\pm$
x%%y	$x \cdot y$
sqrt(x)	$\sqrt{x}$
sqrt(x, y)	$\sqrt[y]{x}$
%prop%	$\propto$
infinity	$\infty$
==	$=$
%==%	$\equiv$
>=	$\geq$
<=	$\leq$
frac(x, y)	$\frac{x}{y}$
x%~~%y	$x \approx y$
x%=~%y	$x \approxeq y$

2 Large-scale operators

Syntax	Meaning
integral(f(x)*dx, a, b)	$\displaystyle \int_{a}^{b} f(x) dx$
sum(f(x), a, b)	$\displaystyle \sum_a^b f(x)$
prod(f(x), a, b)	$\displaystyle \prod_a^b f(x)$
union(A[i], i==1, n)	$\displaystyle \cup_{i = 1}^n A_i$
intersect(A[i], i==1, n)	$\displaystyle \cap_{i = 1}^n A_i$
lim(f(x), x>0)	$\displaystyle \lim_{x \rightarrow 0} f(x)$
min(f(x), x>0)	$\displaystyle \min_{x > 0} f(x)$
bgroup("(",atop(x, y),")")	$x \choose y$

3 Upper and lower markers

Syntax	Meaning
a^b	$a^b$
a[b]	$a_b$

4 Arrows

Syntax	Meaning
%<->%	$\leftrightarrow$
%->%	$\rightarrow$
%<-%	$\leftarrow$
%up%	$\uparrow$
%down%	$\downarrow$
%<=>%	$\Leftrightarrow$
%=>%	$\Rightarrow$
%<=%	$\Leftarrow$
%dblup%	$\Uparrow$
%dbldown%	$\Downarrow$

5 Set operations

Syntax	Meaning
x %subset% y	$x \sub y$
x %subseteq y	$x \subseteq y$
x %supset% y	$x \supset y$
x %supseteq% y	$x \supseteq y$
x %in% y	$x \in y$
x %notin% y	$x \notin y$

6 Derivative notations

Syntax	Meaning
hat(x)	$\hat{x}$
tilde(x)	$\tilde{x}$
dot(x)	$\dot{x}$
bar(X)	$\bar{x}$
widehat(xy)	$\widehat{xy}$
widetilde(xy)	$\widetilde{xy}$
partialdiff	$\partial$
nabla	$\nabla$

7 Special typefaces

Syntax	Meaning
plain(x)	x
bold(x)	x
italic(x)	x
bolditalic(x)	x
underline(x)	x

8 Greek alphabet

Syntax	Meaning	Syntax	Meaning
alpha or symbol(a)	$\alpha$	Alpha or symbol(A)	$\Alpha$
beta or symbol(b)	$\beta$	Beta or symbol(B)	$\Beta$
gamma or symbol(g)	$\gamma$	Gamma or symbol(G)	$\Gamma$
delta or symbol(d)	$\delta$	Delta or symbol(D)	$\Delta$
epsilon or symbol(e)	$\epsilon$	Epsilon or symbol(E)	$\Epsilon$
zeta or symbol(z)	$\zeta$	Zeta or symbol(Z)	$\Zeta$
eta or symbol(h)	$\eta$	Eta or symbol(H)	$\Eta$
theta or symbol(q)	$\theta$	Theta or symbol(Q)	$\Theta$
iota or symbol(i)	$\iota$	Iota or symbol(I)	$\Iota$
kappa or symbol(k)	$\kappa$	Kappa or symbol(K)	$\Kappa$
lambda or symbol(l)	$\lambda$	Lambda or symbol(L)	$\Lambda$
mu or symbol(m)	$\mu$	Mu or symbol(M)	$\Mu$
nu or symbol(n)	$\nu$	Nu or symbol(N)	$\Nu$
xi or symbol(x)	$\xi$	Xi or symbol(X)	$\Xi$
o or symbol(o)	$\omicron$	O or symbol(O)	$\Omicron$
pi or symbol(p)	$\pi$	Pi or symbol(P)	$\Pi$
rho or symbol(r)	$\rho$	Rho or symbol(R)	$\Rho$
sigma or symbol(s)	$\sigma$	Sigma or symbol(S)	$\Sigma$
tau or symbol(t)	$\tau$	Tau or symbol(T)	$\Tau$
upsilon or symbol(u)	$\upsilon$	Upsilon or symbol(U)	$\Upsilon$
phi or symbol(f)	$\phi$	Phi or symbol(F)	$\Phi$
chi or symbol(c)	$\chi$	Chi or symbol(C)	$\Chi$
psi or symbol(y)	$\psi$	Psi or symbol(Y)	$\Psi$
omega or symbol(w)	$\omega$	Omega or symbol(W)	$\Omega$
varphi or symbol(j)	$\varphi$	symbol(V)	$\varsigma$
symbol(v)	$\varpi$	symbol(J)	$\vartheta$