ENG 1181 First-Year Engineering Program College of Engineering Engineering Education Innovation Center First-Year Engineering Program MAT - Introduction P. 1 Agenda  MATLAB Overview  The Command Window  Simple Script Files

ENG 1181 First-Year Engineering Program MATLAB Quizzes Note MATLAB quizzes are assigned in the daily assignment list Material covered on the quizzes will include the most recent preparation materials plus any previous lectures. It is ok to reference the book or slides while taking the quiz. P. 2

ENG 1181 First-Year Engineering Program Slide Format Note the upper right corner indicate pages from the MATLAB book which correspond with the material covered on the slide. P. 3 Introduction Textbook It is very important to review the chapters in the MATLAB book prior to class. They contain complementary information and valuable examples.

ENG 1181 First-Year Engineering Program P. 4 MATLAB is a powerful program for numerical computations, plotting and programming.  Use it as a calculator.  Define variables and use them in calculations.  Use built-in functions.  Plot graphs.  Write and run computer programs.  Perform symbolic mathematics. 1- 3

ENG 1181 First-Year Engineering Program P. 5 MATLAB’s Default Windows

ENG 1181 First-Year Engineering Program P. 6 (The Command Window opens when MATLAB is started) Command window Command prompt 8- 9

ENG 1181 First-Year Engineering Program P. 7 (The Figure Window opens automatically by the plot() command) 7 Figure window

ENG 1181 First-Year Engineering Program P. 8 (The Editor Window is opened from the file menu in the Command Window) 7 Editor window

ENG 1181 First-Year Engineering Program P. 9 (The Help Window can be opened from the Help menu of any of MATLAB windows) 8 Help window

ENG 1181 First-Year Engineering Program P. 10 WORKING IN THE COMMAND WINDOW 8- 9 Place the cursor at the command prompt (>>) to enter a command Press the ‘Enter’ key to execute the command (Line-at-a-time-execution) To correct a previously typed command press the up arrow key ( ) to recall the desired command

ENG 1181 First-Year Engineering Program MATLAB’s Working Directory P. 11 When you first start MATLAB it is a good practice to change the working directory to your N: drive or USB device. You can use the browse icon to locate the directory you want to use

ENG 1181 First-Year Engineering Program P. 12 ARITHMETIC OPERATIONS WITH SCALARS 10 Operation Addition Subtraction Multiplication Right Division Left Division Exponentiation Symbol + - * / \ ^ Example * 3 5 / 3 5 \ 3 = 3 / 5 5 ^ 3

ENG 1181 First-Year Engineering Program P. 13 ORDER OF PRECEDENCE Higher-precedence operations are executed before lower- precedence operations (like Excel or programmable calculators). If two operations have the same precedence, then the expression is executed from left to right. PRECEDENCEOPERATION FirstParentheses (innermost pair first) SecondExponentiation. ThirdMultiplication and division FourthAddition and subtraction 10

ENG 1181 First-Year Engineering Program P. 14 MATLAB AS A CALCULATOR Using numbers: 8 / 2 is executed first >> / 2 ans = 11 Type and press Enter Computer response is executed first >> (7 + 8) / 2 ans = Type and press Enter Computer response 27 ^ 1 and 32 ^ 0.2 are executed first / is executed next + is executed last >> 27 ^ 1 / ^ 0.2 ans = 11 >> 27 ^ (1 / 3) + 32 ^ 0.2 ans = 5 1 / 3 is executed first ^ is executed next + is executed last 11

ENG 1181 First-Year Engineering Program P. 15 DEFINING VARIABLES A variable becomes defined when a value is assigned to it using the assignment operator, =. Once a variable is defined, the computer remembers and stores its value. The variable can then be used in further calculations, used to create new variables, passed into functions. The value of a variable can be modified at any time. >> a = 8 a = 8 >> B = 12 B = 12 Type and press Enter Computer response >> a + B ans = 20 >> a / B ans = >> d = a * B d = 96 >> sqrt(d) ans =

ENG 1181 First-Year Engineering Program P. 16 THE ASSIGNMENT OPERATOR >> x = 3 x = 3 Note: In algebra this expression (x=x+5) is invalid since it implies: 0 = 5. >> x = x + 5 x = 8 MATLAB assigns a new value to x, which is the old value (3) plus The statement: ‘x + 4 = 30’ Is not valid. Matlab does not solve for x >> x + 4 =30 ??? x + 4 = 30 But, the statement ‘x = 30 – 4’ is valid (the number 26 is assigned to x) >> x = x = 26 Assigns the value 3 to variable x.

ENG 1181 First-Year Engineering Program P. 17 RULES ABOUT VARIABLES NAMES  Can be up to 63 characters long.  Must begin with a letter.  Can contain letters, digits, and the underscore character (no spaces).  MATLAB is case sensitive; it distinguishes between UPPERCASE and lowercase letters. For example, 'number‘, ‘NUMBER’, and 'Number' are NOT the same variable.  It is good practice to make the variable name descriptive For example, ‘avg_score’ or ‘avgScore’ instead of ‘a’ 18

ENG 1181 First-Year Engineering Program P. 18 RULES ABOUT VARIABLES NAMES Avoid naming variables names that are used by MATLAB  Names of MATLAB functions: exp, sin, cos, sqrt, max, min, sum, etc.  Names of MATLAB-defined variables: π (accurate to 2.2 * 10 ^ -16) (the solution from the most recent calculation) Etc.  Note that e is not a MATLAB-defined variable (use exp) 18 pi ans

ENG 1181 First-Year Engineering Program P. 19 MATLAB BUILT-IN MATH FUNCTIONS exp(x)exponential (e x ) log(x) natural logarithm (log base “e”, written ln in math expressions) log10(x) base 10 logarithm (log in math expressions) sqrt(x) square root abs(x) absolute value NOTE: For trigonometric functions, x is in radians sin(x), cos(x), asin(x), acos(x), tan(x), cot(x) For each trig function there is an equivalent, e.g. sind(x) where x is in degrees

ENG 1181 First-Year Engineering Program Built-in Functions Here are some examples of using MATLAB built-in functions: P. 20 >> sin(pi / 4) ans = >> sqrt(169) ans = 13 >> log10(10000) ans = 4 MATLAB has hundreds of built-in functions (this will be discussed in future lectures). More functions are listed in section 1.5 of the text.

ENG 1181 First-Year Engineering Program Example Calculate the value of this function for x=30 degrees: cos 2 x sinx + tan(x/2) / √3x In the command window: >>x=30(Assigns the value 30 to x) >>x=x*pi/180(Converts degrees to radians) >>cos(x)^2*sin(x)+tan(x/2)/sqrt(3*x) P. 21

ENG 1181 First-Year Engineering Program Script files What if you wanted do a lengthy calculation many times. What’s the chance of a typo causing an error? MATLAB allows you to save any series of commands in a file and will execute the commands sequentially as if they were typed directly into the command window. These files are called script files.

ENG 1181 First-Year Engineering Program Example with Script file Suppose we created a script file called trig_calc which contained the following: Line 1: x=x*pi/180 Line 2: cos(x)^2*sin(x)+tan(x/2)/sqrt(3*x) Then we would only have to type the following into the command window: >>x=30 >>trig_calc The result would be displayed in the command window

ENG 1181 First-Year Engineering Program SCRIPT FILE  Using a script file is convenient because it can be…  edited (corrected and/or changed)  executed many times with reliable results  saved, then opened at a later date  sent to others to use  Script files are also called M-files because the extension.m is used when they are saved

ENG 1181 First-Year Engineering Program THE M-FILE EDITOR/DEBUGGER WINDOW The commands of the script file are typed line-by-line. The lines are numbered automatically A new line starts when the Enter key is pressed. The Run Icon

ENG 1181 First-Year Engineering Program EXAMPLE OF A SCRIPT FILE % Example of a script file % This file calculates the square of x x = sin(pi / 4) y = x ^ 2 Define x Store result in y Typing ‘%' at the beginning of a line designates the line as a comment  comments are not executed 79

ENG 1181 First-Year Engineering Program SAVING A SCRIPT FILE  Once the script file is completed, it must be saved. In our class use Save As to your N:\ or USB drive. This should be the same as the working directory you specified when you started MATLAB.  The name of the script file follows the rules for names of variables in MATLAB  Can be up to 63 characters long.  Must begin with a letter.  Can only contain letters, digits, and the underscore character (no spaces).  Case sensitive. 78

ENG 1181 First-Year Engineering Program RUNNING A SCRIPT FILE  A script file can be executed from the Editor Window by clicking on the Run icon (this saves the m-file before running).  A script file can also be executed from the Command Window by typing its name and pressing Enter Refer pp in the book about other ways to change the Current Directory or the Search Path.

ENG 1181 First-Year Engineering Program EXAMPLE OF RUNNING A SCRIPT FILE % Example of a script file % This file calculates the square of x x = sin(pi / 4) y = x ^ 2 Script file: >> Test1 x = y = >> Command window: Enter script file name MATLAB response Save script file as Test1

ENG 1181 First-Year Engineering Program SOME USEFUL COMMANDS 10, 19 Clears the command window Clears all variables from memory Clears only variables x, y and z Careful, this command only clears x >> clc >> clear >> clear x y z >> clear x, y, z >> x = 5 x = 5 >> x = 5; >> Typing a semi-colon (;) at the end of a line of input prevents the output from being displayed in the command window

ENG 1181 First-Year Engineering Program OUTPUT FROM A SCRIPT FILE  When a script file runs, output that is generated is displayed in the Command Window  Output is displayed automatically if a statement does not end with a semicolon. Many times you don’t want all outputs to be displayed in the command window.  Output can also be displayed intentionally by using the disp() command

ENG 1181 First-Year Engineering Program THE disp() COMMAND disp(A) disp(‘text’) string disp() adds a ‘line feed’ to the end of it’s input. So, any following output appears on a new line. Displays the value of the variable A. Displays the text (string) that is enclosed within the single quotes

ENG 1181 First-Year Engineering Program DISPLAY FORMATS The format command controls how output numbers appear on the screen. Input numbers can be typed in any format. >> format short (default) Fixed-point with 4 decimal digits >> format long Fixed-point with 15 decimal digits >> format short e e+001 Scientific with 4 decimal digits >> format bank Two decimal digits (like money) Note: These commands affect the output only they do not affect the precision of the number in memory Other formatting options are discussed in section 1.4 of the text >> format short >> format long >> format short e >> format bank

ENG 1181 First-Year Engineering Program Homework Example clc disp ('Student, Joe') disp ('EG167, Seat 99') disp ('Assignment 1') disp ('Problem 4') prob4a = cos(5*pi … … Script File Student, Joe EG167, Seat 99 Assignment 1 Problem 4 prob4a = … Command Window Submit a printout of both the Script File and the Command Window