# 测试KaTeX显示效果

$$x = {-b \pm \sqrt{b^2-4ac} \over 2a}.$$

$${\rm grad}\varphi=\frac{\partial\varphi}{\partial x}e_1+\frac{\partial\varphi}{\partial y}e_2+\frac{\partial\varphi}{\partial z}e_3=\nabla\varphi$$

Thus we can write a vector $${\bf a}\in\mathbb {R}^2$$as

$${\bf a}=\left(\begin{matrix}a_1\\a_2\end{matrix}\right)$$

$$\left(\begin{matrix}a_1\\a_2\end{matrix}\right)+\left(\begin{matrix}b_1\\b_2\end{matrix}\right)=\left(\begin{matrix}a_1+b_1\\a_2+b_2\end{matrix}\right)$$

For a vector $${\bf v}\in\mathbb{ R}^n$$,the euclidean norm of $$\mathbf{v}$$is defined as,
$$\parallel\mathbf{v}\parallel=\left(\sum_{i=1}^{n}{v_i^2}\right)^\frac{1}{2}=\sqrt{\left\langle \mathbf{v,v}\right\rangle}$$

$$\boxed{\vec{s}}$$ , $$\overrightarrow{suv}$$

import matplotlib.pyplot as plt
import numpy as np

x=np.linspace(0,20,100)
plt.plot(x, np.sin(x))
plt.show()