Introduction to Matlab Programming with Applications

Transcription

1 Introduction to Matlab Programming with Applications Zheng-Liang Lu Department of Computer Science and Information Engineering National Taiwan University Matlab 256 Summer 2015

2 Class Information Official Web page d /matlab 256.html Lecture notes will be uploaded right before class. Note that the lecture notes are organized in English. Contact information If you have any question, please contact me via . facebook Zheng-Liang Lu 1 / 70

3 Prerequisites No programming experience required. It would be helpful if you have some programming experiences. Linear Algebra is strongly recommended. Matlab refers to Matrix laboratory. Linear Algebra is widely used in numerical analysis and quantitative methods. Please be informed that you should consider other classes if you want to learn any advanced computer science courses. 1 I promise to keep everything simple in this class. 2 1 After you get familiar with one of programming languages, you may consider some advanced courses such as algorithms, computational statistics, digital image processing, and even financial engineering. 2 Simple is not easy.... Easy is a minimum amount of effort to produce a result.... Simple is very hard. Simple is the removal of everything except what matters.... See here. Zheng-Liang Lu 2 / 70

4 Grading To pass the class, you need at least 70 pts in the end of class. Programming assignment (50 pts) Final project/exam (50 pts) Please be noted that you preserve the right 3 to refund before the 5th lecture. 3 Zheng-Liang Lu 3 / 70

5 Final Project Topic: anything if you are interested in or working on. Requirement: you should use Matlab as the main programming language. Your grade depends on the following aspects: Problem definition Innovation 4 Completion Goal: To solve a problem by formulating the problem, organizing into an algorithm, writing the codes To get familiar with programming concepts To gain the experiences in order to learn more programming languages on your own 4 No copy-and-paste. You should understand the program thoroughly. Zheng-Liang Lu 4 / 70

6 Final Exam On-site programming 8 to 10 questions Open everything No communication with classmates and your friends Zheng-Liang Lu 5 / 70

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8 What Is Programming? Programming is the way of writing a sequence of instructions to tell a computer to perform a specific task. A sequence of instructions program A set of well-defined notations is used to write a program programming language The person who writes a program a programmer Zheng-Liang Lu 7 / 70

9 In Practice Programming is about providing a solution to a real-world problem using computational models supported by the programming language. The solution is a program. The program must be practical and effective. Zheng-Liang Lu 8 / 70

10 Programs A (computer) program is a sequence of instructions, written in an artificial language, to perform a specified task with a computer. They are almost everywhere such that you can name it. For example, Computer virus Games 5 Operating systems 6 Social networking 7 Differences: goal, functionality, algorithms, complexity Try Pong. 6 Such as Windows 8.1, UNIX, Linux, Mac OS X, Android, and ios. 7 Such as Facebook, twitter, and so on. 8 A measure of difficulty for a specific algorithm. Zheng-Liang Lu 9 / 70

11 How and Where The Programs Run The programs are activated from the disk into the main memory. Now we call them the processes. 9 All the instructions are executed in CPU, while the data is stored in the registers. The results are written back to the main memory and further stored into the disk after the processes are terminated. 9 A formal terminology used in Operating System. Zheng-Liang Lu 10 / 70

12 Memory Hierarchy See Figure 1-9 in Bryant, p. 14. Zheng-Liang Lu 11 / 70

13 Process Virtual Address Space See Figure 1-13 in Bryant, p. 18. Zheng-Liang Lu 12 / 70

14 Programming Languages A programming language is an artificial language designed to communicate with a machine by instructions. Programming languages syntax Express algorithms Control the behavior of a machine Matlab belongs to the post 3rd-generation programming languages. 1st generation: machine code 2nd generation: assembly code 3rd generation: high-level programming languages Beyond 3rd generation Zheng-Liang Lu 13 / 70

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16 1st-Generation Programming Languages The fact is, Computers understand instructions only in binary format, which is a sequence of 0s and 1s. A computer has a fixed set of basic instructions that it understands. Each computer has its own set of instructions. So, the earliest programming language is machine-dependent, so called machine code. Zheng-Liang Lu 15 / 70

17 Pros: Most efficient for machines Cons: Hard to program for human Not portable Still widely (and occasionally) used in programming lower level functions of the system, such as drivers, interfaces with firmware and hardware devices. Zheng-Liang Lu 16 / 70

18 2nd-Generation Programming Languages An assembly language uses mnemonics 12 to represent instructions as opposed to the binary (0s and 1s) used in machine language. The code can be read and written by a programmer. Yet, it is still machine-dependent. For each machine, there is one-to-one correspondence between an instruction in machine language and assembly language for a given computer architecture. 13 To run on a computer, it must be converted into a machine readable form, a process called assembly. Zheng-Liang Lu 17 / 70

19 More often find use in extremely intensive processing such as games, video editing, graphic manipulation/rendering. Note that machine language and assembly language are also known as low-level languages. 12 Easy to recognize and memorize. 13 For example, x86. See any textbook for computer organization or architecture. Zheng-Liang Lu 18 / 70

20 3rd-Generation Programming Languages The high-level programming languages use English-like words, mathematical notation, and punctuation to write programs. They are closer to the written languages that humans are familiar with. The translation is accomplished by a compiler, an interpreter, or a combination of both. Pros: Portable, machine-independent Support structured programming Human-friendly Such as C 14, C++ 15, and Java Zheng-Liang Lu 19 / 70

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22 What Can A Program Do? A program is an implementation of an algorithm expressed in a specific programming language. The more important question is, do what? Zheng-Liang Lu 21 / 70

23 Algorithm In A Nutshell An algorithm is any well-defined computational procedure that takes some value, or set of values, as input and produces some value or set of values, as output. Simply put, an algorithm is a procedure that solves a particular type of problems, such as a cookbook. Zheng-Liang Lu 22 / 70

24 Properties of Algorithms Typical properties of any algorithm are summarized as follows: Input Statements: definiteness Instructions: effectiveness Number of steps: finiteness 17 Output: correctness Note that an algorithm is not necessarily expressed in a specific programming language. Instead, one can express an algorithm in some human language using a programming language format. 17 Alan Turing ( ) Zheng-Liang Lu 23 / 70

25 Example Organize an algorithm that finds the greatest element in the input list. Input: A (a list of n integers) Output: x (the greatest element in A) 1 x <-- A(1) 2 for i <-- 1 ~ n 3 if A(i) > x 4 x <-- A(i) 5 end 6 end 7 return x Zheng-Liang Lu 24 / 70

26 Computers are good at following instructions, but not at reading your mind. Donald Knuth (1938-) Zheng-Liang Lu 25 / 70

27 What is Matlab? In my view, Matlab is a powerful and simple math software: Powerful: programmable, fruitful toolboxes 18 available Simple: don t need to worry about the machine, easy to draw a graph The only thing you need to provide is Zheng-Liang Lu 26 / 70

28 Algorithms! This is a screenshot of The Social Network (2010). Zheng-Liang Lu 27 / 70

29 Conclusions Program design algorithm + programming language Algorithm idea, steps Programming language Chinese, English In this class, we will learn Matlab and some algorithms which are the core of programming world. Zheng-Liang Lu 28 / 70

30 Father of Matlab Cleve Moler Zheng-Liang Lu 29 / 70

31 Get started to implement your idea with Matlab. Zheng-Liang Lu 30 / 70

32 1 >> Lecture 1 2 >> 3 >> -- Overview of Matlab 4 >> Zheng-Liang Lu 31 / 70

33 Learning a new language is harmless. It gives you new ideas and insights. Yukihiro Matsumoto ( 松本行弘 ) (1965 ) Zheng-Liang Lu 32 / 70

34 Contents Environment Script editor Variable types Scalar variable Numeric arrays Character arrays (String) Cell arrays Structure arrays Built-in arithmetic functions Zheng-Liang Lu 33 / 70

35 Working Environment Zheng-Liang Lu 34 / 70

36 Command Window You can give a command in the Command Window. Let s try a greeting, Hello, Matlab. 1 >> disp('hello, Matlab.'); disp prints the string as input in the parenthesis. A string is single-quoted in Matlab. Convention in the slides: Boxes are the listings for programs. Words and sentences highlighted in red are important. Words in blue are reserved words. Bold words in black are functions. Zheng-Liang Lu 35 / 70

37 Tips for Learning Matlab Don t be frustrated: 紅字是必經之路 犯錯是為了下一次的成功作預演 Matlab interrupts your program when a syntax error occurs. lookfor is used to look for the commands related to the key word you give. 1 >> lookfor display disp - Display array. 4 display - Display array. 5 error - Display message and abort function. 6 warning - Display warning message; disable or enable... warning messages Zheng-Liang Lu 36 / 70

38 help returns the usage of a command 1 >> help disp 2... Help browser provides detail of commands with examples. Google is your friend. Zheng-Liang Lu 37 / 70

39 Script Editor We often write a program in the script editor. Save the program in.m file..m files are used as scripts and functions. A script is a complete program which contains the input data and can be executed directly. A function is a program which may need input data when being called in other programs. (why?) Zheng-Liang Lu 38 / 70

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41 helloworld.m Let s create a.m file with the following code lines: 1 % This is the comment section. 2 clear; % Clear all variables stored in Workspace. 3 clc; % Clear the screen. 4 % main program 5 disp('hello, world.'); Note that The lines which begins with % are regarded as the comments. Comments are not executed. clear is used to release the variables. clc cleans the command window. Zheng-Liang Lu 40 / 70

42 Save 20 and press F5 21 to run the script. Do not give a script file the same name as a variable. (Why?) Do not give a filename with blanks in the middle. If the.m file is not at the current folder when you execute it, Matlab will ask: 1 Change folder 2 Add to Path Pool You can run helloworld.m later just by calling helloworld in the command window. 1 >> helloworld 2 3 Hello, world. 20 ctrl + s 21 Autosave before execution. Zheng-Liang Lu 41 / 70

43 Comments In Scripts Anything following a % is seen as a comment. Press ctrl + r to comment. ctrl + t to de-comment. To comment a block of lines, %{ %}. The first contiguous comment becomes the script s help document. 1 >> help helloworld 2 3 This is the comment section. Why documents? Helpful for both the programmers and users. Avoid wasting time later. Zheng-Liang Lu 42 / 70

44 Variables Variable is used to store a value, assigned by variable name = expression. x = x + 1 is correct. (Why?) Actually, the assignment operator is used to put a value in the variable, from right to left. For example, let a = 10, b = 20. Then a + b = >> a = 10; 2 >> b = 20; 3 >> a + b 4 5 ans = 6 30 ans is the default variable if you don t assign one for it. Zheng-Liang Lu 43 / 70

45 If you drop the semicolon (;) in the line, then the result will appear in the command window, say, 1 >> a = a = Note that you may not drop semicolons in other programming languages. The variable name is suggested to begin with a letter of the alphabet. Cannot begin with a number, e.g. 1x is wrong. Cannot have a blank, e.g. x 1 is wrong. Cannot have +-*\%, e.g. x%1 Zheng-Liang Lu 44 / 70

46 Matlab is case-sensitive 22, e.g. A and a are different. The length of name is limited to 63 characters 23. namelengthmax returns what this maximum length is. We avoid to use names of reserved words 24 and built-in functions. The reserved words cannot be used as a variable, e.g. for, if, and end. i = 1 and j = 1 by default. If you set i = 1, then i = 1 until you clear i. Variable names should always be mnemonic In general, programming languages are case-sensitive, but some are not, e.g. Fortran. 23 Windows 7 (64-bit) in this case 24 Try iskeyword. 25 To assist your memory. Zheng-Liang Lu 45 / 70

47 Data Type and Casting Everything is encoded by binary numbers (0 and 1) in a certain size. Particularly, the integers and real numbers, actually floating points, are different data types. (Why?) Different types of variables occupy different size of memory. All numeric variables are stored as the type double 26 by default. Variables defined in type char are of size 2 bytes. Variables defined in type logical are of size 1 bytes. whos shows variables that have been defined in the command window. cast converts one variable to another type. int8, int16, int32, and int64 are the integer types bytes = 64 bits. Zheng-Liang Lu 46 / 70

48 Computational Limits In Matlab, it is a common convention to use e to identify a power of 10, e.g. 1e5 = 100, 000. Zheng-Liang Lu 47 / 70

49 Scalar Variables A scalar is a single number. A scalar variable is a variable that contains a single number. x is said to be a scalar variable if x R 1 or C 1. The complex field, denoted by C, contains all the complex numbers, in form of a + bi, where i = 1, and a, b R 1. Try x = 1 + i in the command window. In math, C 1 is equivalent to R 2. So, x is stored as the type double with 16 = 8 2 bytes. Zheng-Liang Lu 48 / 70

50 Scalar Arithmetic Operators See Table 2.1 Arithmetic Operations Between Two Scalars in Moore, p. 21. Zheng-Liang Lu 49 / 70

51 Display Format See Table Numeric display formats in Palm, p. 15. Zheng-Liang Lu 50 / 70

52 Arrays One of the strengths of Matlab is its ability to handle collections of numbers, called arrays, as if they were a single variable. An array is a systematic arrangement of objects, such as Row vectors: x R 1 n for any positive integer n. Column vectors: x R n 1 for any positive integer n. Matrices: A R n m for any positive integers n, m. Zheng-Liang Lu 51 / 70

53 The dimension of a general array is unlimited without regarding to the limit of memory space. You can create an n m k matrix for any positive integers n, m, k,.... (Try.) For example, let A be a matrix. Then it takes MB in memory space. Actually, all the arrays are stored in a continuous memory space. Zheng-Liang Lu 52 / 70

54 Example 1 >> row vector = [1 2 3] % [... ] is used in arrays. 2 3 row vector = >> column vector = [1;2;3] % semicolon is used to change... rows column vector = >> matrix=[1 2 3; 4 5 6; 7 8 9] % define a 3-by-3 matrix 16 Zheng-Liang Lu 53 / 70

55 17 matrix = Zheng-Liang Lu 54 / 70

56 Some special matrices can be initialized by the following functions: Zheng-Liang Lu 55 / 70

57 Referring to Matrix Elements Index of arrays in Matlab starts from 1 not 0. Note that it does start from 0 in C. Matrices can be indexed in two ways: Subscripted indexing Linear indexing: matrices are arrays stored in a continuous memory space in column major order. 1 >> matrix(2,3) % using subscripted indexing 2 3 ans = >> matrix(8) % using linear indexing 7 8 ans = 9 6 Zheng-Liang Lu 56 / 70

58 Example: Deleting Elements 1 >> matrix(2, [1 3]) 2 3 ans = >> matrix(:, 1) = [] % delete the first column vector matrix = Zheng-Liang Lu 57 / 70

59 Automatic Initialization of Array linspace(,, ) initializes a linear vector of values. 1 >> x = linspace(0,10,5) % start, end, points 2 3 x = You can also use colon operator (:) to create a vector. For example, 1 >> x = 0 : 2 : 10 % start : increment : end 2 3 x = logspace initializes logarithmically spaced values. (Try.) Zheng-Liang Lu 58 / 70

60 Example: Invalid Vector Creation 1 >> x = 1 : -1 : x = 4 5 Empty matrix: 1-by-0 We will use this property later. Zheng-Liang Lu 59 / 70

61 Strings Recall that a string in Matlab is single-quoted. Let x = Arthur. Then x stores a string. 1 >> x = 'Arthur' 2 3 x = 4 5 Arthur 6 7 >> Actually, x is an array whose elements store a character in order. Zheng-Liang Lu 60 / 70

62 Tricks with Arrays It is easy to manipulate the arrays, including strings. For example, 1 >> x = 'Arthur'; 2 >> x = [x ' meets Matlab.'] % string concatenation 3 4 x = 5 6 Arthur meets Matlab. 7 8 >> x=[x; 'This is Matlab252.'] % Cause an error? But it is not useful to store strings in different length. Also, an array cannot contain data of different types! Zheng-Liang Lu 61 / 70

63 Cell Array A cell array is a data type with indexed data containers called cells, where each cell can contain any type of data. Cell arrays commonly contain either lists of text strings, combinations of text and numbers, or numeric arrays of different sizes. Zheng-Liang Lu 62 / 70

64 Example 1 >> A(1,1) = {'This is the first cell.'}; 2 >> A(1,2) = {[5 + j * 6, 4 + j * 5]}; 3 >> A(2,1) = {[1 2 3; 4 5 6; 7 8 9]}; 4 >> A(2,2) = {{'Tim'; 'Chris'}} ; 5 >> A 6 7 A = 8 9 'This is the first cell.' [1x2 double] 10 [3x3 double] {2x1 cell } celldisp(c) recursively displays the contents of a cell array C. Zheng-Liang Lu 63 / 70

65 Referring to Cell Array Using curly braces, { }, for the subscripts will reference the contents of a cell; this is called context indexing. Using parentheses, ( ), for the subscripts references the cell; this is called cell indexing. 1 >> A{1} 2 ans = 3 This is the first cell. % check this type 4 >> A(1) 5 ans = 6 'This is the first cell.' % check this type More details can be found in here. Zheng-Liang Lu 64 / 70

66 Structure Array A structure array is a data type that groups related data using data containers called fields. Each field can contain any type of data. You can access data of the structure array by dot operator in the form of structname.fieldname. For example, 1 >> student.name = 'Arthur'; 2 >> student.id = 'd '; 3 >> student.scores = [80, 90, 100]; 4 >> student % show the content of student 5 >> 6 7 student = 8 Zheng-Liang Lu 65 / 70

67 9 name: 'Arthur' 10 id: 'd ' 11 scores: [ ] fieldnames returns the names of the fields contained in a structure variable. rmfield removes a field from a structure. You can pass structures to functions. More details can be found here. They are extremely useful in applications such as Matlab GUI and database management. Zheng-Liang Lu 66 / 70

68 Symbols In Workspace Zheng-Liang Lu 67 / 70

69 Basic Math Functions See Table in Palm, p Zheng-Liang Lu 68 / 70

70 Trigonometric Functions 30 Recall that 1 rad = 180 π. 30 See Table Zheng-Liang in Palm, Lu p / 70

71 Summary: 31 Parentheses ( ) Arithmetic, e.g. (x + y)/z. Input arguments of a function, e.g. sin(1), exp(1). Array addressing, e.g. A(1) refers to the first element in array A. Square brackets [ ]: only used in array operations e.g. x = [ ]. Curly brackets { }: only used to declare a cell array e.g. A = { This is Matlab class., x}. 31 Thanks to a lively class discussion (Matlab-237) on April 16, Zheng-Liang Lu 70 / 70