# SAJID GUL KHAWAJA Introduction to MATLAB 1. Introduction What is MATLAB ? MATLAB is a computer program that combines computation and visualization power.

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1 SAJID GUL KHAWAJA Introduction to MATLAB 1

2 Introduction What is MATLAB ? MATLAB is a computer program that combines computation and visualization power that makes it particularly useful tool for engineers. MATLAB is an executive program, and a script can be made with a list of MATLAB commands like other programming language. MATLAB Stands for MATrix LABoratory. The system was designed to make matrix computation particularly easy. The MATLAB environment allows the user to: manage variables import and export data perform calculations generate plots develop and manage files for use with MATLAB. 2

3 MATrix LABoratory 3 Advantages of MATLAB Ease of use Platform independence Predefined functions Plotting Disadvantages of MATLAB Can be slow Commercial software

4 MATLAB Screen Command Window type commands Current Directory View folders and m- files Workspace View program variables Double click on a variable to see it in the Array Editor Command History view past commands save a whole session using diary 4

5 Variables No need for types. i.e., All variables are created with double precision unless specified and they are matrices. After these statements, the variables are 1x1 matrices with double precision int a; double b; float c; Example: >>x=5; >>x1=2; 5

6 Variables Types Variable types Numeric Logical Character and string Cell and Structure Function handle 6

7 Variables (cont…) Variable names: Must start with a letter Youll get an error if this doesnt happen May contain only letters, digits, and the underscore _ MATLAB is case sensitive, i.e. one & OnE are different variables. MATLAB only recognizes the first 31 characters in a variable name. Assignment statement: Variable = number; Variable = expression; Example: >> tutorial = 1234; >> tutorial = 1234 tutorial = 1234 NOTE: when a semi-colon ; is placed at the end of each command, the result is not displayed. 7

8 Variables (cont…) Dont name your variables the same as functions min, max, sqrt, cos, sin, tan, mean, median, etc Funny things happen when you do this MATLAB reserved words dont work either i, j, eps, nargin, end, pi, date, etc i, j are reserved as complex numbers initially Will work as counters in my experience so they can be redefined as real numbers Give meaningful (descriptive and easy-to-remember) names for the variables. Never define a variable with the same name as a MATLAB function or command. Give meaningful (descriptive and easy-to-remember) names for the variables. Never define a variable with the same name as a MATLAB function or command. 8

9 Special Variables Special Values MATLAB includes a number of predefined special values. These values can be used at any time without initializing them. These predefined values are stored in ordinary variables. They can be overwritten or modified by a user. If a new value is assigned to one of these variables, then that new value will replace the default one in all later calculations. >> circ1 = 2 * pi * 10; >> pi = 3; >> circ2 = 2 * pi * 10; Never change the values of predefined variables. 9

10 Special Variables (cont…) Special variables: ans : default variable name for the result pi: = ………… eps: = e-016, smallest amount by which 2 numbers can differ. Inf or inf :, infinity NaN or nan: not-a-number Commands involving variables: who: lists the names of defined variables whos: lists the names and sizes of defined variables clear: clears all varialbes, reset the default values of special variables. clear name: clears the variable name clc: clears the command window clf: clears the current figure and the graph window. 10

11 Interactive Commands Format of output Defaults to 4 decimal places Can change using format statement format long changes output to 15 decimal places 11

12 Operators (arithmetic) +addition -subtraction *multiplication /division ^power complex conjugate transpose 12

13 Operators Scalar arithmetic operations OperationMATLAB form – Exponentiation: ^ a b a^b – Multiplication: *ab a*b – Right Division: / a / b = a/ba/b – Left Division: \ a \ b = b/aa\b – Addition: +a + ba+b – Subtraction: -a – ba-b MATLAB ignores white space between variables and operators 13

14 Operators (relational, logical) == Equal to ~= Not equal to < Strictly smaller > Strictly greater <= Smaller than or equal to >= Greater than equal to & And operator | Or operator 14

15 Operators (Element by Element).*element-by-element multiplication./element-by-element division.^element-by-element power 15

16 Order of Operations Parentheses Exponentiation Multiplication and division have equal precedence Addition and subtraction have equal precedence Evaluation occurs from left to right When in doubt, use parentheses – MATLAB will help match parentheses for you 16

17 Vectors, Matrices and Arrays Vectors Array Operations Matrices 17

18 Arrays The fundamental unit of data in MATLAB Scalars are also treated as arrays by MATLAB (1 row and 1 column). Row and column indices of an array start from 1. Arrays can be classified as vectors and matrices. 18 Vectors, Matrices and Arrays

19 Vector: Array with one dimension Matrix: Array with more than one dimension Size of an array is specified by the number of rows and the number of columns, with the number of rows mentioned first ( For example: n x m array ). Total number of elements in an array is the product of the number of rows and the number of columns. 19 Vectors, Matrices and Arrays

20 Arrays 20 Variables and Arrays Array : A collection of data values organized into rows and columns, and known by a single name. Row 1 Row 2 Row 3 Row 4 Col 1Col 2Col 3Col 4Col 5 arr(3,2)

21 a=3x2 matrix 6 elements b=[ ]1x4 array 4 elements, row vector c= x1 array 3 elements, column vector a(2,1)=3b(3)=3c(2)=3 Row #Column # 21

22 Vectors A row vector in MATLAB can be created by an explicit list, starting with a left bracket, entering the values separated by spaces (or commas) and closing the vector with a right bracket. A column vector can be created the same way, and the rows are separated by semicolons. Example: >> x = [ *pi 0.5*pi 0.75*pi pi ] OR x = [ *pi, 0.5*pi, 0.75*pi, pi] x = >> y = [ 0; 0.25*pi; 0.5*pi; 0.75*pi; pi ] y = x is a row vector. y is a column vector. 22

23 Vectors (cont…) Vector Addressing – A vector element is addressed in MATLAB with an integer index enclosed in parentheses. Example: >> x(3) ans = st to 3 rd elements of vector x The colon notation may be used to address a block of elements. (start : increment : end) start is the starting index, increment is the amount to add to each successive index, and end is the ending index. A shortened format (start : end) may be used if increment is 1. Example: >> x(1:3) ans = NOTE: MATLAB index starts at 1. 3 rd element of vector x 23

24 Vectors Some useful commands: x = start:end create row vector x starting with start, counting by one, ending at end x = start:increment:end create row vector x starting with start, counting by increment, ending at or before end length(x) returns the length of vector x y = x transpose of vector x dot (x, y) returns the scalar dot product of the vector x and y. 24

25 Arrays and Matrices 25 Initializing with Shortcut Expressions first: increment: last Colon operator: a shortcut notation used to initialize arrays with thousands of elements >> x = 1 : 2 : 10; >> angles = (0.01 : 0.01 : 1) * pi; Transpose operator: () swaps the rows and columns of an array >> g = [1:4] ; >> h = [ g g ]; h=h=

26 Long Array, Matrix t =1:10 t = k =2:-0.5:-1 k = B = [1:4; 5:8] x =

27 Matrices Addressing Matrix Addressing: -- matrixname(row, column) -- colon may be used in place of a row or column reference to select the entire row or column. recall: f = h = Example: >> f(2,3) ans = 6 >> h(:,1) ans =

28 Generating Vectors/Matrices from functions zeros(M,N)MxN matrix of zeros ones(M,N)MxN matrix of ones rand(M,N)MxN matrix of uniformly distributed random numbers on (0,1) x = zeros(1,3) x = x = ones(1,3) x = x = rand(1,3) x =

29 Subarrays 29 Subarrays The end function: When used in an array subscript, it returns the highest value taken on by that subscript. arr3 = [ ]; arr3(5:end) is the array [ ] arr4 = [ ; ; ]; arr4(2:end, 2:end)

30 Subarrays (cont…) 30 Subarrays Assigning a Scalar to a Subarray: A scalar value on the right-hand side of an assignment statement is copied into every element specified on the left-hand side. >> arr4 = [ ; ; ]; >> arr4(1:2, 1:2) = 1 arr4 =

31 Array Operations Scalar-Array Mathematics For addition, subtraction, multiplication, and division of an array by a scalar simply apply the operations to all elements of the array. Example: >> f = [ 1 2; 3 4] f = >> g = 2*f – 1 g = Each element in the array f is multiplied by 2, then subtracted by 1. 31

32 Array Operations (cont…) Element-by-Element Array-Array Mathematics. OperationAlgebraic FormMATLAB Additiona + b Subtractiona – b Multiplicationa x ba.* b Division a b a./ b Exponentiationabab a.^ b Example: >> x = [ ]; >> y = [ ]; >> z = x.* y z = Each element in x is multiplied by the corresponding element in y. 32

33 Matrices Some Useful Commands Length(A) returns the larger of the number of rows or columns in A. Size(A) for a m x n matrix A, returns the row vector [m,n] containing the number of rows and columns in matrix. TransposeB = A Identity Matrixeye(n) returns an n x n identity matrix eye(m,n) returns an m x n matrix with ones on the main diagonal and zeros elsewhere. Addition and subtractionC = A + B C = A – B Scalar Multiplication B = A, where is a scalar. Matrix MultiplicationC = A*B Matrix InverseB = inv(A), A must be a square matrix in this case. rank (A) returns the rank of the matrix A. Matrix PowersB = A.^2 squares each element in the matrix C = A * A computes A*A, and A must be a square matrix. Determinantdet (A), and A must be a square matrix. A, B, C are matrices, and m, n, are scalars. 33

34 The input function displays a prompt string in the Command Window and then waits for the user to respond. my_val = input( Enter an input value: ); in1 = input( Enter data: ); in2 = input( Enter data:,s); Initializing with Keyboard Input 34

35 The disp (Array/String) function >> disp( 'Hello' ) Hello >> disp(5) 5 >> disp( [ Hello ' World!' ] ) Hello World! >> name = World!'; >> disp( [ 'Hello ' name ] ) Hello World! Displaying Data in MATLAB 35

36 Display Windows Graphic (Figure) Window Displays plots and graphs Created in response to graphics commands. M-file editor/debugger window Create and edit scripts of commands called M-files. 36

37 Plotting For more information on 2-D plotting, type help graph2d Plotting a point: >> plot ( variablename, symbol) the function plot () creates a graphics window, called a Figure window, and named by default Figure No. 1 Example : Complex number >> z = j; >> plot (z,.) 37

38 Basic Task: Plot the function sin(x) between 0 x 4π Create an x-array of 100 samples between 0 and 4 π. Calculate sin(.) of the x-array Plot the y-array >>x=linspace(0,4*pi,100); >>y=sin(x); >>plot(y) 38

39 Display Facilities plot(.) stem(.) Example: >>x=linspace(0,4*pi,100); >>y=sin(x); >>plot(y) >>plot(x,y) Example: >>stem(y) >>stem(x,y) 39

40 Display Facilities title(.) xlabel(.) ylabel(.) >>title(This is the sinus function) >>xlabel(x (secs)) >>ylabel(sin(x)) 40

41 x = 0:pi/100:2*pi; y = sin(x); plot(x,y) xlabel('x = 0:2\pi') ylabel('Sine of x') title('Plot of the Sine Function') 41 MATLAB Graphs

42 t = 0:pi/100:2*pi; y1=sin(t); y2=sin(t+pi/2); plot(t,y1,t,y2) grid on 42 Multiple Graphs

43 Selection Programming Flow Control Loops 43

44 Flow Control (if/else) Simple if statement: if logical expression commands end Example: (Nested) if d <50 count = count + 1; disp(d); if b>d b=0; end Example: (else and elseif clauses) if temperature > 100 disp (Too hot – equipment malfunctioning.) elseif temperature > 90 disp (Normal operating range.); elseif (Below desired operating range.) else disp (Too cold – turn off equipment.) end 44

45 Switch, Case, and Otherwise switch input_num case -1 input_str = 'minus one'; case 0 input_str = 'zero'; case 1 input_str = 'plus one'; case {-10,10} input_str = '+/- ten'; otherwise input_str = 'other value'; end switch input_num case -1 input_str = 'minus one'; case 0 input_str = 'zero'; case 1 input_str = 'plus one'; case {-10,10} input_str = '+/- ten'; otherwise input_str = 'other value'; end More efficient than elseif statements Only the first matching case is executed 45

46 Loops for loop for variable = expression commands end while loop while expression commands end Example (for loop): for t = 1:5000 y(t) = sin (2*pi*t/10); end Example (while loop): EPS = 1; while ( 1+EPS) >1 EPS = EPS/2; end EPS = 2*EPS o the break statement break – is used to terminate the execution of the loop. 46

47 M-Files The M-file is a text file that consists a group of MATLAB commands. MATLAB can open and execute the commands exactly as if they were entered at the MATLAB command window. To run the M-files, just type the file name in the command window. (make sure the current working directory is set correctly) All MATLAB commands are M-files. So far, we have discussed the execution of commands in the command window. But a more practical way is to create a M-file. 47

48 User-Defined Function Add the following command in the beginning of your m-file: function [output variables] = function_name (input variables); NOTE: the function_name should be the same as your file name to avoid confusion. calling your function: -- a user-defined function is called by the name of the m-file, not the name given in the function definition. -- type in the m-file name like other pre-defined commands. Comments: -- The first few lines should be comments, as they will be displayed if help is requested for the function name. the first comment line is reference by the lookfor command. 48

49 result = function_name( input ); –abs, sign –log, log10, log2 –exp –sqrt –sin, cos, tan –asin, acos, atan –max, min –round, floor, ceil, fix –mod, rem help elfun help for elementary math functions Built-in MATLAB Functions 49

50 Getting Help For help type one of following commands in the command window: help – lists all the help topic help topic – provides help for the specified topic help command – provides help for the specified command help help – provides information on use of the help command helpwin – opens a separate help window for navigation lookfor keyword – Search all M-files for keyword 50

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