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• Statistical Inference 统计推断
• Statistical Computing 统计计算
• (Generalized) Linear Models 广义线性模型
• Statistical Machine Learning 统计机器学习
• Longitudinal Data Analysis 纵向数据分析
• Foundations of Data Science 数据科学基础

## 物理代写|电磁学代写electromagnetism代考|The Electrostatic System of Units

The mechanical units in the ESU system are the cgs units (centimeter, gram, and second). The unit of charge, the statcoulomb, is derived from Coulomb’s law.

We write the expression of the force acting between two charges $q_1$ and $q_2$ as follows:
$$F=|\mathbf{F}|=K \frac{q_1 q_2}{r^2}=\frac{q_1 q_2}{r^2}$$
where $r=$ distance between the two charges. In expression (2.2.1), we set the proportionality constant $K=1$, and the unit charge is defined in such a way that two similar unit charges separated by $1 \mathrm{~cm}$ in vacuum repel each other with the force of 1 dyne. Dimensionally,
\begin{aligned} {\left[q^2\right] } &=\left[F r^2\right]=M L^3 T^{-2} \ {[q] } &=L T^{-1} \sqrt{M L} \end{aligned}
The field and the potential of a point charge in empty space are given by
$$E=\frac{q}{r^2}$$
and
$$\phi=\frac{q}{r}$$
respectively. Therefore, the dimensions of $E$ and $\phi$ are given by
\begin{aligned} &{[E]=\frac{1}{T} \sqrt{\frac{M}{L}}} \ &{[\phi]=\frac{1}{T} \sqrt{M L}} \end{aligned}
The charge of the electron is $-4.80286 \times 10^{-10}$ statcoulomb.

## 物理代写|电磁学代写electromagnetism代考|The International System of Units

Before introducing the SI system of units, we shall make some observations on the system of mechanical units. In such a system, three basic units are chosen, a unit of mass, a unit of length, and a unit of time. This is one of many possible choices, and the number of units chosen (three) does not represent the minimum number of units needed. In fact it is possible to set up a mechanical system of units in which all mechanical quantities can be expressed in terms of length and time. ${ }^1$

A similar situation is present with Coulomb’s law. If we set the proportionality constant equal to the pure number 1 , then charges can be expressed dimensionally in terms of $M, L$, and $T$. This is the case for the electrostatic system of units. On the other hand, in the SI system, in addition to the three basic units of length (meter, m), mass (kilogram, $\mathrm{kg}$ ), and time (second, s), a fourth basic unit is used, a unit of current called ampere (A). This unit is defined as follows: “That constant current which, if maintained in two straight parallel conductors of infinite length, of negligible cross section, and placed one meter apart in vacuum, would produce between these conductors a force equal to $2 \times 10^{-7}$ newton per meter of length. ${ }^2$ “In the SI system the coulomb is a derived unit defined as ampere $\times$ second. In the SI units we express Coulomb’s law as follows:
$$F=\frac{1}{4 \pi \varepsilon_0} \frac{q_1 q_2}{r^2} \quad \text { (2.2.4) }$$
where $1 / 4 \pi \varepsilon_0$ is a proportionality constant and the charges are expressed in coulombs. The dimensions of $\varepsilon_0$ are easily derived from (2.2.4); the result of measurements gives us

We can also work with some other quantities. Since the electric field is the ratio of a force to a charge
$$[E]=\frac{\text { newton }}{\text { coulomb }}=\frac{\text { newton-meter }}{\text { coulomb-meter }}=\frac{\text { joule }}{\text { coulomb-meter }}=\frac{\text { volt }}{\text { meter }}$$

# 电磁学代考

## 物理代写|电磁学代写electromagnetism代考|The Electrostatic System of Units

ESU 系统中的机械单位是 cgs 单位 (厘米、克和秒)。电荷单位 statcoulomb 源自库仑定律。

$$F=|\mathbf{F}|=K \frac{q_1 q_2}{r^2}=\frac{q_1 q_2}{r^2}$$

$$\left[q^2\right]=\left[F r^2\right]=M L^3 T^{-2}[q] \quad=L T^{-1} \sqrt{M L}$$

$$E=\frac{q}{r^2}$$

$$\phi=\frac{q}{r}$$

$$[E]=\frac{1}{T} \sqrt{\frac{M}{L}} \quad[\phi]=\frac{1}{T} \sqrt{M L}$$

## 物理代写|电磁学代写electromagnetism代考|The International System of Units

$$F=\frac{1}{4 \pi \varepsilon_0} \frac{q_1 q_2}{r^2}$$

$$[E]=\frac{\text { newton }}{\text { coulomb }}=\frac{\text { newton-meter }}{\text { coulomb-meter }}=\frac{\text { joule }}{\text { coulomb-meter }}=\frac{\text { volt }}{\text { meter }}$$

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## MATLAB代写

MATLAB 是一种用于技术计算的高性能语言。它将计算、可视化和编程集成在一个易于使用的环境中，其中问题和解决方案以熟悉的数学符号表示。典型用途包括：数学和计算算法开发建模、仿真和原型制作数据分析、探索和可视化科学和工程图形应用程序开发，包括图形用户界面构建MATLAB 是一个交互式系统，其基本数据元素是一个不需要维度的数组。这使您可以解决许多技术计算问题，尤其是那些具有矩阵和向量公式的问题，而只需用 C 或 Fortran 等标量非交互式语言编写程序所需的时间的一小部分。MATLAB 名称代表矩阵实验室。MATLAB 最初的编写目的是提供对由 LINPACK 和 EISPACK 项目开发的矩阵软件的轻松访问，这两个项目共同代表了矩阵计算软件的最新技术。MATLAB 经过多年的发展，得到了许多用户的投入。在大学环境中，它是数学、工程和科学入门和高级课程的标准教学工具。在工业领域，MATLAB 是高效研究、开发和分析的首选工具。MATLAB 具有一系列称为工具箱的特定于应用程序的解决方案。对于大多数 MATLAB 用户来说非常重要，工具箱允许您学习应用专业技术。工具箱是 MATLAB 函数（M 文件）的综合集合，可扩展 MATLAB 环境以解决特定类别的问题。可用工具箱的领域包括信号处理、控制系统、神经网络、模糊逻辑、小波、仿真等。

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