Laura Broussard, Ph.D.

1
COS 131 Computing for EngineersCh. 2 Getting
Started with MATLAB

• Laura Broussard, Ph.D.
• Professor

2
Ch. 2 Getting Started with MATLAB

1. Introduction
2. Programming Language Background
3. Basic Data Manipulation
4. The MATLAB User Interface
5. Scripts
6. Engineering Example

3
I. Introduction

• The name MATLAB is a contraction of Matrix
  Laboratory.
• MATLAB was developed for engineers to create,
  manipulate, and visualize matrices
• (matrix lots of numbers arranged in a
• rectangular array).

4
I. Introduction

• Fundamental components of MATLAB
• Accepts one instruction at a time in text form
  and implements the logic of that instruction
• (similar to a calculator)
• Large library of modules that provide high-level
• capabilities for processing data.
• Large collection of toolboxes
• (Toolbox separate application program that
  provides graphical capabilities
• A Graphical User Interface (GUI) that lets users
  assemble and implement programs that solve
  specific problems.

5
I. Introduction

• Advantages over compiled languages
• MATLAB is an interpreted language.
• Problem-solving can be much faster than for
  compiled
• languages.
• Excels in numerical and especially matrix
  calculations
• A wide set of toolboxes for graphical
  problem-solving
• Build your own GUIs with MATLABs GUIDE
• (Graphical User Interface Development
  Environment)
• Graphic output is high quality
• Can use in professional reports

6
I. Introduction

• Compiled programs are better for
• Large computing projects, especially where there
  are multiple programmers
• Major GUI and graphics-based programs

7
Ch. 2 Getting Started with MATLAB

1. Introduction
2. Programming Language Background
3. Basic Data Manipulation
4. The MATLAB User Interface
5. Scripts
6. Engineering Example

8
II. Programming Language Background

1. Abstraction
2. Algorithms
3. Programming Paradigms

9
II. Programming Language Background

• Abstraction
• Abstraction expressing a quality apart from
  a particular implementation.
• Example Exacto, maroon, Standup stapler
• or stapler

10
Programming Language Background

• Abstraction
• Two types for computer programming
• data abstraction
• To convert from degrees Celsius to Kelvin, you
  add 273 to the temperature.
• Specific is 33C, abstract is temperature
• 2. procedural abstraction
• He drove home from the office.
• Specific is turn left, drive 3 blocks, turn
  right,
• Abstract is drive home

11
II. Programming Language Background

• Algorithms
• Algorithm A sequence of instructions for
  solving a problem.
• Algorithms vary in level of abstraction.
• Baking cookies instructions
• For your grandmother high level of abstraction
• For a beginner low level
• Computer program problems Start with abstract
  algorithms,

12
II. Programming Language Background

• Algorithms
• Algorithms abstraction in problem-solving
• Method Divide entire problem into subproblems.
• Solutions to subproblems are algorithms.
• Process of solving and assembling subproblems
  into
• solution for entire problem is also an alogorithm
  of higher
• abstraction.
• Process Start with big picture and go down
• Initial attempt at entire problem - high level of
  abstraction.
• Successive attempts for subprograms at lower and
  lower levels of abstraction until they work.

13
II. Programming Language Background

• Programming Paradigms
• paradeigma to show alongside (Greek)
• Everyday meaning
• a set of assumptions, concepts, values, and
  practices that constitutes a way of viewing
  reality for the community that shares them,
  especially in an intellectual discipline
• Computer Programming
• a codified set of practices allowing the
  community of computer professionals to frame
  their ideas.

14
II. Programming Language Background

• Programming Paradigms
• Three different types of paradigms
• Functional Programming
• Procedural Programming
• Object Oriented Programming or OOP
• Side effect - when a function returns a result
  and also changes other objects, it has side
  effects
• Useful, but problematic
• Computer paradigms allow to different degrees

15
II. Programming Language Background

• Programming Paradigms
• Functional Programming
• Every programming operation is actually
  implemented as a function call without side
  effects (program surroundings do not change by
  the function call)
• Can prove solution to be mathematically correct
• Of some value in theoretical computer science
• Languages Lisp and Forth

16
II. Programming Language Background

• Programming Paradigms
• Procedural Programming
• Programs are sequences of operations on data
  items that are generally accessible to all
  programs.
• Side effects are possible but considered bad
  programming practice
• Languages FORTRAN, C, and MATLAB

17
II. Programming Language Background

• Programming Paradigms
• Object-Oriented Programming or OOP
• Objects (data, variables) packaged together with
  the methods or functions that manipulate those
  data items ? everything is an object
• Side effects explicitly managed
• MATLAB exhibits OOP-like traits, but you wont
  need to use them!
• Languages C, Ada, and Java

18
Ch. 2 Getting Started with MATLAB

1. Programming Language Background
2. Basic Data Manipulation
3. The MATLAB User Interface
4. Scripts
5. Engineering Example

19
III. Basic Data Manipulation

• Starting and Stopping MATLAB
• Assigning Values to Variables
• Data Typing
• Classes and Objects

20
Basic Data Manipulation

• Starting and Stopping MATLAB
• Practice Exercise 2.1 (p. 21b in text)
• Starting and stopping MATLAB
• Macintosh
• Start Click icon on Dock
• End
• Menu MATLAB/Quit
• Click red circle Upper-Left
• Type quit or exit after prompt in Command
  Window
• (next slide)
• PCs?

21
III. Basic Data Manipulation
Note the double cursor to the left side of the
command window
MATLAB Screen
22
III. Basic Data Manipulation

• Definition of Variable
• A representative for a number (algebra)
• A symbolic name associated with a value and
• whose value may be changed (programming)
• Significantly different meanings
• ? be careful!

23
III. Basic Data Manipulation

• Assigning values to Variables
• Point of confusion MATLABs syntax for assigning
  values to variables looks like an algebra
  equation. Its not!
• Example z x y
• In programming this means take the values stored
  in x and in y, sum them, and place them in the
  memory location defined as z.
• If x or y has not been assigned a value, get an
  error.
• In algebra, if z and y are known, can solve for x.

24
III. Basic Data Manipulation

• Assigning values to Variables
• Example z x y
• Note True only for this statement.
• Programmer might change this in the next
  instruction z 4x y
• Some programs (Pascal and Ada) use the
• to denote the difference

25
Basic Data Manipulation

• Assigning values to Variables
• Practice Exercise 2.2 (p. 23t in text)
• Assigning Variables
• Set radius equal to 49
• Retrieve radius. Default variable is ans.
• Terminate lines by pressing

Enter
26
III. Basic Data Manipulation

• Assigning Values to Variables
• Variable names may contain any combination
  of
• uppercase and lowercase letters
• numbers
• special characters _ (underscore) and
  (dollar sign)
• Underscore represents a space (not
  allowed).
• Be consistent (_ or , not a mix)
• May be really long (100s of characters!)
• First 64 characters must be unique
• Hyphens not allowed file-size (no)
  file_size (yes)

27
III. Basic Data Manipulation

• Assigning Values to Variables
• Style Points
• Choose names that describe variables content
• Example for the velocity of an object, not just
  v
• velocity_in_feet_per_second
• or
• VelocityInFeetPerSecond

28
III. Basic Data Manipulation

• Data Typing
• How does MATLAB treat the data stored in a
  variable?
• Computer languages may be categorized as
• Untyped
• Typed
• Interpreted or untyped languages determine type
  of data in a variable by the data that is there.
• Typed languages require user to declare the data
  type.

29
III. Basic Data Manipulation

• Data Typing
• Data types
• char (assign by single quotes around
  characters)
• numeric (numbers)
• MATLAB may handle different data types the same
  way

30
III. Basic Data Manipulation

• Data Typing
• Exer 2.3 Performing basic mathematical
  operations

• gtgt radius 49
• radius
• 49
• gtgt radius 1
• ans
• 50
• gtgt radius 'radius of a circle
• radius
• radius of a circle
• gtgt radius 1
• ans
• Columns 1 through 12
• 115 98 101 106

MATLAB allows radius to be both types Initial
radius is a numeric type. Second radius is a
char type. radius 1 depends on the type of
data radius is!
Good or bad? Good Can assign a variable type
without advance preparation. Bad A typo can
make a new variable Other program runtime
errors
31
III. Basic Data Manipulation

• Data Typing
• Typed languages require the programmer to declare
  the name and data type of a variable
• Compiler controls the appropriate use of each
  variable
• Weak typing programmer uses only the normal
  data types
• Strong typing programmer defines specific data
  types with a limited set of permissible
  interactions

32
III. Basic Data Manipulation

• Classes and Objects
• Variables have two attributes
• Value - determined by what is assigned
• Data type (class) - the type of data
  stored
• Example myShoeSize 9.5
• MATLAB considers
• the value contained in myShoeSize to be 9.5
• its class to be double (the default numeric
  type).
• A value of data is also called an object.

33
Ch. 2 Getting Started with MATLAB

1. Introduction
2. Programming Language Background
3. Basic Data Manipulation
4. The MATLAB User Interface
5. Scripts
6. Engineering Example

34
IV. The MATLAB User Interface

• MATLAB Interface Basics
• Several display windows are visible
• Default view
• Left side Current Folder
• Middle Command Window
• Right Workspace and History Windows (stacked)
• Other windows (Editor, Graphing) open as needed

35
IV. The MATLAB User Interface
Close icon
Current directory
Workspace Window
Command window
Macintosh Display
Command history
36
V. The MATLAB User Interface

• MATLAB can be used in two modes
• Command mode when you need immediate responses
  to specific MATLAB commands
• Commands not saved permanently
• Edit mode where you develop practical solutions
  to real problems
• Create and execute a text file of commands

37
V. The MATLAB User Interface

• Command Window
• Exercise 2.4 Using the Command window
• Smith text, page 29, top

38
V. The MATLAB User Interface

• Command History Window
• Records the commands you issued in the command
  window in chronological order
• Retains list of commands when Command Window is
  cleared (clc)
• Window retains a list of commands from previous
  MATLAB sessions
• Clear by menu Edit / Clear Command History

39
V. The MATLAB User Interface

• Command History Window
• Exercise 2.5 Using the Command History Window
• Smith text, p. 28t

40
V. The MATLAB User Interface

• Workspace Window
• Keeps track of the variables you use
• Columns display information about variables
• the name of the variable
• the current value
• class (data type) with an icon and entry
• others information can be selected

41
V. The MATLAB User Interface

• Workspace Window and Variables
• Exercise 2.6 Showing more details in the
  workspace window, p. 28b
• Exercise 2.7 Defining other variables, p. 29m
• Exercise 2.8 Creating a vector, p. 29b

42
V. The MATLAB User Interface

• Workspace Window and Variables
• Notes on vectors and matrices
• Semicolons are used to separate rows
• Can recall the values for any variable by just
  typing in the variable name
• If you suppress the workspace window, you can
  still find out what variables have been defined
  by using the who and whos commands.
• who lists the variable names
• whos lists the variable names together with
  their size and class

43
V. The MATLAB User Interface

• Workspace Window and Variables
• Exercise 2.9 Creating a 3 x 4 matrix, p. 30b
• Exercise 2.10 Recalling values for variables,
  p31t
• Exercise 2.11 Using the who and whos command, p.
  33b

44
V. The MATLAB User Interface

• Current Directory Window
• This window gives the current directory path
  where MATLAB is retrieving and storing your files

Note how unintuitive the Current directory
window is. Your eye skips right over it.
45
V. The MATLAB User Interface

• Variable Editor
• Double-clicking on any variable in the Workspace
  window automatically launches a document window
  containing the Array editor.
• Array editor allows you to enter new data or
  change existing data
• A semicolon at the end of data entry to a
  variable suppresses the display of those values
  in the command window.

46
V. The MATLAB User Interface

• Variable Editor
• Exercise 2.12 Creating a two-dimensional
  matrix,
• p. 33t

47
V. The MATLAB User Interface

• Graphics Window
• Created automatically when a MATLAB command
  requests a graph.
• Additional graphics requests will overwrite the
  contents of the current graphic window unless you
  request MATLAB to open a new Graphics window

48
V. The MATLAB User Interface

• Graphics Window
• Created automatically when a MATLAB command
  requests a graph.
• Additional graphics requests will overwrite the
  contents of the current graphic window unless you
  request MATLAB to open a new Graphics window
• Exercise 2.13 Creating a graph, p. 33b

49
The MATLAB User Interface

• Graphics Window

50
V. The MATLAB User Interface

• Editor Window
• The text editor for MATLAB
• Create or modify text files here
• Opened by choosing File gt New gt M-File
• Lets you type and save a series of commands
  without executing them
• Also open the editor window by double-clicking a
  file name in the current directory window or by
  typing
• gtgt edit ltfile_namegt in the command window

51
Ch. 2 Getting Started with MATLAB

1. Introduction
2. Programming Language Background
3. Basic Data Manipulation
4. The MATLAB User Interface
5. Scripts
6. Engineering Example

52
VI. Scripts

• Text files
• Section describes the basic mechanism for
  creating, saving, and executing scripts
  (programs) as m-files
• Use text files as a permanent means of saving
  scripts
• A script is like writing an email message lines
  of text written in a smart editor

53
VI. Scripts

• Creating Scripts
• A combination of executable instructions
  interpreted by MATLAB and comment statements that
  document the script help readers understand
  what the program is doing
• Comments are created by placing a percent symbol,
  , at the beginning of any text you desire to
  be a comment good through the end of the line in
  which it was created comment lines are green in
  editor window
• Uses the extension .m for script files
• Exercise 2.14 Creating a script, p. 37b

54
VI. Scripts

• Creating Scripts

See line by line description of this simple
MATLAB program on page 36 of the Smith text.
55
VI. Scripts

• The Current Directory
• Must name and save the script in a directory
  where MATLAB can find it
• MATLAB expects a path like c\MATLABxxx\work
• You can provide MATLAB with a different directory
  to use in the current directory window you will
  then need to use the browse button pointed out
  earlier to retrieve the m-file
• Exercise 2.15 Saving a script, p. 39t

56
VI. Scripts

• Running Scripts
• Can run a script using any of the following
  methods
• Type the name of the script in the command window
• Choose the Debug gt Run menu item in the MATLAB
  editor window
• Press the F5 key when the script is visible in
  the editor. This automatically saves the script
  before executing it.
• Exercise 2.16 Running a script, p39b

57
VI. Scripts

• Debugging Scripts
• Uses breakpoints places in your program where
  you want to verify your code is doing what you
  want it to
• Click the small dash between the line number and
  the start of the text line in the Editor window
• Can examine the content of variables by passing
  the mouse slowly over the variable in the
  Workspace window or variable in the Editor window
• Watch for inadvertently typed semicolons does
  weird things to your programs!
• Exercise 2.17 Debugging a script, p. 40b

58
Ch. 2 Getting Started with MATLAB

1. Introduction
2. Programming Language Background
3. Basic Data Manipulation
4. The MATLAB User Interface
5. Scripts
6. Engineering Example

59
VI. Engineering Example Spacecraft Launch

• Problem Assuming that the spacecraft uses all
  its fuel to achieve a vertical velocity u at
  25,000 feet, what is the value of u for the
  spacecraft to reach outer space?

60
VI. Engineering Example Spacecraft Launch

• Solution
• Two parts to this problem
• Converting units to the metric system
• Choosing and solving an equation for motion under
  constant acceleration

61
VI. Engineering Example Spacecraft Launch

• Part 1 converting units to the metric system
• 1 inch 2.54 cm
• We have

62
VI. Engineering Example Spacecraft Launch

• MATLAB code for converting units to the metric
  system

Note line by line description of code on pages
41-42 of text.
63
VI. Engineering Example Spacecraft Launch

• MATLAB code for solving for the equation
• Need the following
• Initial and final altitudes from which you can
  compute the distance traveled s
• Motion is under constant acceleration, the force
  of gravity, g
• Just to reach outer space, the final velocity, v,
  is 0
• Initial velocity, u, is needed

64
VI. Engineering Example Spacecraft Launch

• MATLAB code for solving for the equation
• Equation for motion under constant acceleration
  connecting u, v, s, and a is

65
VI. Engineering Example Spacecraft Launch

• Complete MATLAB code for solving for the equation

Note line by line description of code on pages
41-43 of text.