Chapter 1 Introduction to MATLAB

Transcription

1 EGR115 Introduction to Computing for Engineers Introduction to MATLAB from: S.J. Chapman, MATLAB Programming for Engineers, 5 th Ed Cengage Learning Topics Introduction: Computing for Engineers 1.1 The Advantages of MATLAB 1.2 Disadvantages of MATLAB 1.4 Using MATLAB as a Calculator

2 Slide 1 of 14 Introduction: Computing for Engineers Father of Computing: Charles Babbage ( ) Charles Babbage ( ), an English mathematician, is best remembered for originating the first concept of a programmable computation machinery * (original concept of today s computer). *Note on the Application of Machinery to the Computation of Astronomical and Mathematical Tables, Royal Astronomical Society (1822). The Babbage Analytical Engine ( ) The mill executed the operations on values retrieved from the store (CPU). The store used punched cards adapted from the Jacquard to specify input (MEMORY). The machine eats its own tail the output redirects to the input for further instructions. ALU (Arithmetic Logic Unit) Computer s Central Processing Unit (CPU) that performs operations on binary numbers (bitwise math). Multiple ALUs can be found in a single CPU. In some processors, the ALU is divided into AU (Arithmetic Unit) and LU (Logical Unit). Are today s most advanced computers POWERFUL ENOUGH to do anything? NASA Columbia ( ERAU Prescott: Advanced Computing & Simulations Laboratory (ACSL)

3 1.1/1.2 The Advantages/Disadvantages of MATLAB Slide 2 of 14 The Purpose of EGR115 (Introduction to Computing for Engineers) It is NOT the purpose of this course to make you learn how to use MATLAB. MATLAB is simply the choice of computer language (or software) for you to learn how to understand and apply computing (design/develop/debug/deploy computer programs) for an effective engineering problem solutions. The MATLAB (MATrix LABoratory) A special-purpose computer program originally developed to perform engineering and scientific calculations. As the name implies, the software was originally developed for matrix calculations (Algebra/Calculus applications). Today, MATLAB has been grown to be one of the most used engineering/scientific software tools. The origins of MATLAB: Advantages & Disadvantages of MATLAB MATLAB is an INTERPRETER (no need to compile: means, ease of use), platform independent, predefined functions, device-independent plotting, and capable for developing a Graphical User Interface (GUI). MATLAB is an INTERPRETER (no need to compile: means, slower than compiled language) and the software is prohibitively expensive for personal (and academic research) use. Any solution(s)?: MATLAB Just-In-Time (JIT) Compiler / GNU Octave

4 Slide 3 of 14 The MATLAB Desktop (this is where you begin...) Current Folder Browser shows a list of the files in the current folder Workspace Browser shows variables defined in workspace MATLAB Editor Details Window displays properties of file selected above MATLAB Command Window NOTE: the textbook is written for MATLAB 2014b The fundamental unit of data in MATLAB is the ARRAY: an array is a collection of data values organized into rows & columns (MATRIX) and given a single name. As an interpreter, you can just quickly write up your computer code and run it: no need to compile your code (means: decode language instructions into command so that you can execute your developed code in a computer). The MATLAB Desktop The MATLAB desktop is the collection of 4 windows: COMMAND WINDOW, COMMAND HISTORY, CURRENT FOLDER, and WORKSPACE. When you create (new) or open (import and load an existing file) a MATLAB script (knows as M-FILE ), a MATLAB EDITOR opens. As you simply type, save, and run MATLAB script, you can execute your program (getting a result). MATLAB is an interpreter: no need to compile your program! Just run the program: if the program is good, you ll get a result. If the program is bad, you ll get an error. The MATLAB Command Window A user can enter interactive MATLAB commands at the command prompt (>>). The MATLAB accepts commands, interpret/execute it, and then output result(s). For example, >> diameter = 10 diameter = 10 Command Window >> area = (pi/4)*(diameter^2) area =

5 Slide 4 of 14 MATLAB Toolstrip (selection of tools & commands) Dock/Undock Each Individual Window The MATLAB windows can be either docked (to form a desktop) or undocked (to be used as an individual window). Just click the top-right-corner of each window The PANELS icon (in Quick Access Toolbar) also controls the MATLAB Windows The MATLAB Toolstrip The MATLAB toolstrip conveniently provides you quick access tabs to some key control functions, based on the categorized groups: HOME, PLOTS, APPS, EDITOR, PUBLISH, and VIEW. The most commonly used tab will (most likely) be the EDITOR tab: this is going to be used for developing your own MATLAB script (m-file) by typing the code, open/save the m-file, test run/time/debug the code. The MATLAB Command History The Command History Window appears when you click the PANELS icon (in Quick Access Toolbar: above) or just simply hit up arrow key ( ) while you type in the Command Window. Commands remain in the list until they are deleted (it is kept even after you close the program).

6 Slide 5 of 14 Script (the M-File : the program code you ll develop/run) a b c d The MATLAB Script File ( M-File ) Instead of typing commands directly in the Command Window, a series of commands can be placed into a file, and the entire file can be executed by typing its name in the Command Window. Open a new script and save as calc_area.m Type the same commands into the MATLAB Editor (save the file after you re done typing) Type calc_area into MATLAB Command Window Command Window >> calc_area diameter = 10 area = The MATLAB script file ( m-file ) can be created (new) by choosing: (a) new script under HOME tab (then, the MATLAB Editor will automatically open) or (if a script is already open in MATLAB Editor): (b) new => script under EDITOR tab (then, a new m-file will be added into the MATLAB Editor). The MATLAB Editor can be used in docked mode (c) or undocked (individual window) mode (d). The MATLAB m-file is a simple ASCII text file (.txt): thus, one can even create a MATLAB m-file by using any text editor (i.e., notepad) and can import into MATLAB (file extension must be changed from.txt into.m ). ASCII = American Standard Code for Information Interchange (ASCII code is a numerical representation of a character set: computers can only understand binary numbers...)

7 Slide 6 of 14 MATLAB Workspace (this is where your variables are...) The MATLAB Workspace Using the MATLAB Editor, create a simple script: Editor % calc_area2.m % Simple MATLAB M-File Demo radius = 2.5; area = pi * radius^2; string = [ The area of the circle is num2str(area)]; disp(string); Then, run the script in Command Window: Command Window >> calc_area2 The area of the circle is Executing the script will create variables in Workspace, namely: area, radius, and string. A list of variables (ARRAYS) in MATLAB Workspace can be generated with the whos command: Command Window >> whos Name Size Bytes Class Attributes Area 1x1 8 double Radius 1x1 8 double String 1x32 64 char

8 Slide 7 of 14 EXAMPLE 1-1 Calculate and plot sin(x) versus x for the range of 0 x 6 by using MATLAB script (M-file). % example_1_1_sin_x.m % % This is the very first MATLAB M-File % Calculation & Plot the function sin(x) % Range 0 <= x <=6 (increment of 0.1) % x = 0:0.1:6 y = sin(x) plot(x,y) The MATLAB Figure Window When a plotting command is executed, MATLAB automatically opens a new window (the FIGURE WINDOW) and completes the plot within the figure window. The strong plotting capability is one of the unique advantages of MATLAB, making this software extremely effective for engineering and scientific problem solutions. (Network\prfsvs01.erau.edu\Courses (T):\EGR115\Hayashibara\EXAMPLES\) example_1_1_sin_x.m

9 Slide 8 of 14 EXAMPLE 1-2 Calculate and plot cos(x) versus x for the range of 0 x 6 by using MATLAB script (M-file). Then, can we plot BOTH sin(x) (from example 1-1) and cos(x) on the same figure window? % example_1_2_cos_x.m % % This is the 2nd MATLAB M-File % Plot the function sin(x) & cos(x) % Range 0 <= x <=6 (increment of 0.1) % Then plot BOTH sin(x) & cos(x) % clc clear all close all x = 0:0.1:6 y1 = sin(x) y2 = cos(x) plot(x,y1,x,y2) (Network\prfsvs01.erau.edu\Courses (T):\EGR115\Hayashibara\EXAMPLES\) example_1_2_cos_x.m

10 Slide 9 of 14 Do-It-Yourself (DIY) EXERCISE 1-1 Develop a MATLAB script (M-File) to plot the function: y x 2e 0.2x for the range of 0 x 10. % exercise_1_1_exp_x.m %... Use the MATLAB Editor to create a new empty M-File, type statements, save the file with the name exercise_1_1_exp_x.m. Then, execute the program by typing the M-File name (exercise_1_1_exp_x) in the Command Window. What results can you get? exercise_1_1_exp_x.m

11 Slide 10 of 14 Do-It-Yourself (DIY) EXERCISE 1-2 Develop a MATLAB script (M-File) to plot the function: 2log10x y x for the range of 0 x 10. Then, plot BOTH exp(x) (from exercise 1-1) and log(x) on the same figure window. % exercise_1_2_log_x.m % clc clear all close all... exercise_1_2_log_x.m

12 Slide 11 of 14 MATLAB Current Folder Browser and Documentation The MATLAB Workspace Browser / Array Editor The MATLAB workspace variables (arrays with m n size) can be seen in Workspace Browser. After executing example_1_2_cos_x.m, you ll see: If you double click each variable, you can view/edit actual numerical values allocated within the array (stored in the memory of a computer you are running). The MATLAB Current Folder Browser and Documentation You can set the working directory of your MATLAB session by choosing the current folder. A comprehensive MATLAB documentation can be accessed easily at search box.

13 Slide 12 of 14 Do-It-Yourself (DIY) EXERCISE 1-3 Answer the followings (use your own words to explain): (a) What is the purpose of the MATLAB Command Window? The Edit Window? The Figure Window? (b) List the different ways that you get help in MATLAB. (c) What is a workspace? How can you determine what is stored in a MATLAB workplace? (d) How can you clear the contents of a workspace? How can you clear the current command window? How can you close figure window(s)? The MATLAB Set Path As you start working MATLAB project, you ll find it would be useful to set a particular working directory for quick access. You can do that by HOME => Set Path. (a) The MATLAB command window takes interactive user command inputs. A user can enter a command at the command prompt (>>). Then the MATLAB interprets/executes the command and outputs result(s). Instead of typing commands manually, a user can develop a script file (the MATLAB M-File) and execute the script by type the name of the script in the command window. The MATLAB command window is the core component of the MATLAB environment. The MATLAB Editor allows the user develop (new) and edit (existing) MATLAB scripts (M-Files). The Editor also can let the user test run/time/debug/deploy the script. The MATLAB figure window allows the plot (2-D/3-D) within the window, upon execution of plot commands. (b) Use MATLAB help browser (built-in MATLAB documentation) At the command window, type help command/function name At the command window, type lookfor command/function name (c) The MATLAB workspace is a part of computer memory used to store variables defined by a user. A list of variables in the current workspace can be generated by whos command. You can view/edit actual values stored within each variable by using MATLAB workspace browser and array editor. (d) clear = clear variables in workspace clear all = clear all local/global user-defined variables and all functions from the symbol table clc = clear contents of current command window close all = close all currently open figure window

14 Slide 13 of Using MATLAB as a Calculator EXAMPLE 1-3 (a) Suppose that x = 3 and y = 4. Use MATLAB to evaluate the following 2 2 expression: x y x y 2 (b) Calculate the volume of a cylinder of radius r (0.1) and length l (0.5) by using MATLAB command window. Note that: Area is A = r 2 and Volume is V = Al Using the MATLAB Editor, develop simple scripts (m-files): Editor % example_1_3a.m x = 3 y = 4 ((x^2)*(y^2))/(x-y)^2 % example_1_3b.m r = 0.1; l = 0.5; area = pi*r^2 volume = area*l Editor Then, run the script in Command Window: >> example_1_3a.m x = 3 y = 4 ans = 144 Command Window >> example_1_3b.m area = volume = Command Window Getting Help in MATLAB 3 Ways to get help in MATLAB: (i) Help browser (built-in MATLAB documentation): The help browser (in Quick Access Toolbar) opens MATLAB documentation (with search options) In command window, type either (ii) help or (iii) lookfor (followed by a specific command/function name) A Few Important MATLAB Commands clc = clear contents of current command window clf = clear contents of current figure window clear = clear variables in workspace clear all = clear all local/global user-defined variables and all functions from the symbol table close all = close all currently open figure window abort (or CTRL+c ) = terminate the current execution of commands diary = record everything done during a MATLAB session (diary filename)

15 Slide 14 of Using MATLAB as a Calculator exercise_1_4.m Do-It-Yourself (DIY) EXERCISE 1-4 (a) Suppose that x = 2 and y = 1, evaluate the following expressions using MATLAB: 4 3 2x 4 2 y 3 (b) Suppose that u = 2 and v = 3, evaluate the following expressions using MATLAB: u 2v v u v v u 3 v v (c) The distance traveled by a ball falling in the air is given by the equation: x x0 vot 0.5at 2 Use MATLAB (save your program code in M-File script) to calculate the position of the ball x (m) at: Time t = 5 (s) x 0 = 10 (m) v o = 15 (m/s) a = 9.81 (m/s 2 ) Editor Command Window % exercise_1_4.m >> exercise_1_4 % (a) x = 2; ans_a1 = 2 y = -1; ans_a1 = (2*x^3)^(1/4) ans_a2 = i ans_a2 = (2*y^3)^(1/4) % (b) ans_b1 = u = 2; v = 3; ans_b2 = ans_b1 = (4*u)/(3*v) ans_b2 = (2*v^(-2))/((u+v)^2) ans_b3 = ans_b3 = (v^3)/(v^3-u^3) ans_b4 = (4/3)*pi*v^2 ans_b4 = % (c) t = 5; ans_c_x = x0 = 10; v0 = 15; a = -9.81; ans_c_x = x0+v0*t+0.5*a*t^2