### 数学代写|编码理论代写Coding theory代考|ELEN90030

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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

## 数学代写|编码理论代写Coding theory代考|MANIPULATIVE INTRODUCTION TO DOUBLE-ERROR-CORRECTING BCH CODES

We have seen that a linear code is characterized by its parity-check matrix $3 C$. We have also seen that the syndrome of the received sequence is the sum of the columns of $\mathcal{F C}$ corresponding to the error positions. Hence, a linear code is capable of correcting all single-error patterns iff all columns of $3 C$ are different and nonzero. If $\exists C$ has $m$ rows and can correct single errors, then $n \leq 2^{m}-1$. The Hamming codes achieve this bound.

Each digit of a Hamming code may be labeled by a nonzero binary $m$-luple, which is equal to the corresponding column of the $\mathfrak{B C}$ matrix. The $m$ syndrome digits then reveal directly the label of the error (if there is only one) or the binary vector sum of the labels (if there are several).

This labeling idea is so useful that we shall continue to assume that $n=2^{m}-1$
and that the columns of $\Im C$ have been labeled accordingly. Now suppose that we wish to correct all patterns of two or fewer errors. Obviously we need a greater redundancy; that is, $\mathcal{B C}$ must have more rows. Proceeding naĩvely, we suspect that we may need about twice as many parity checks to correct two errors as we need to correct one, so we shall try to find a parity-check matrix $\xi c$ with $2^{m}-1$ columns and $2 m$ rows.

## 数学代写|编码理论代写Coding theory代考|A CLOSER LOOK AT EUCLID’S ALGORITHM

In the previous section we indicated that the decoding of binary $\mathrm{BCH}$ codes requires arithmetic operations in the field of binary polynomials mod some irreducible binary polynomial $M(x)$. From both the theoretical and practical standpoints, Euclid’s algorithm plays a key role in this development.

From the theoretical standpoint, Euclid’s algorithm is used to prove that the factorization of polynomials into irreducible polynomials is unique (except for scalar multiples) over any field and that a polynomial of degree $d$ cannot have more than $d$ roots in any field. This fact is needed to prove that the error locator polynomial $\sigma(z)$ cannot have more roots than its degree. If it did, then the entire decoding procedure sketched in Sec. $1.4$ would be invalid, for several different pairs of error locations might conceivably be reciprocal roots of the same quadratic equation.

From the practical standpoint, Euclid’s algorithm is important because one of its modifications, the method of convergents of continued fractions, provides the basis for one of the most efficient methods for implementing division in finite fields. This method, apparently new, will be detailed in this section and the next.

Euclid’s algorithm is based on the observation that any divisor of $R$ and $r$ must also divide their sum and their difference. Furthermore, since any divisor of $r$ also divides any nonzero multiple of $r$, such as $a r$, then any divisor of $R$ and $r$ must also divide $R \pm a r$. Conversely, any divisor of $r$ and $R \pm a r$ must also divide $(R \pm a r) \mp a r=R$. Hence, if we let $(R, r)$ denote the greatest common divisor (hereafter called ged) of $R$ and $r$, then we have $(R, r)=(r, R \pm a r)$. Consequently, starting from an original pair of elements $R$ and $r$, we can find a new pair of elements which have the same ged. If the multiplier $a$ is judiciously chosen, the problem of finding the ged of the new pair of elements will be easier than the original problem.

## 数学代写|编码理论代写Coding theory代考|LOGICAL CIRCUITRY

The three basic elements used in logical design are the AND gate, the OR gate, and the inverter, which are represented as shown in Fig. 2.01. The AND and OR gates may have several inputs, each of which carries a binary signal having either the value 0 or the value 1 . The output of the AND gate is zero unless all its inputs are ones, in which case the output of the AND gate is also one. The output of the OR gate is one unless all of its inputs are zero, in which case the output of the OR gate is also zero. The inverter, in contrast to the AND and OR gates, has only one input, and its output is the opposite of its input. If its input signal has value 0 , the output has value 1 ; if the input signal has value 1 , the output has value 0 .

In practice, circuits having the logical properties of these three elements may be constructed out of transistors, resistors, diodes, vacuum tubes, and/or other components. Depending on the detailed properties t Starred sections of this book may be skimmed or omitted on first reading.of these components, the overall design will be subject to certain restrictions, called design constraints. For example, there will be maximum numbers of inputs to AND and OR gates and a maximum number of elements through which signals can propagate successively without additional amplification. Typically, every inverter is equipped with an amplifier, but AND and OR gates are not. Design constraints then specify how many AND and/or OR gates may be successively encountered between inverters and in what orders. Since the design constraints depend heavily on the properties of the components, we shall not consider design constraints much further here. If some of our circuits do not satisfy particular design constraints, it may be necessary to insert additional amplifiers (or pairs of successive inverters) into the circuits at certain crucial points.

## 有限元方法代写

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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。