Covenant College October 7, 20151 Laura Broussard, Ph.D. Professor COS 131: Computing for Engineers Ch. 2: Getting Started with MATLAB

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Laura Broussard, Ph.D.

Professor

COS 131: Computing for Engineers

Ch. 2: Getting Started with MATLAB


I. Introduction

II. Programming Language Background

III. Basic Data Manipulation

IV.The MATLAB User Interface

V. Scripts

VI.Engineering Example

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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).

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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.

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I. Introduction• Advantages over compiled languages:

– MATLAB is an interpreted language. Problem-solving can be much faster than for compiledlanguages.

– Excels in numerical and especially matrix calculations

– A wide set of toolboxes for graphical problem-solving

– Build your own GUIs with MATLAB’s GUIDE (Graphical User Interface Development

Environment)

– Graphic output is high quality Can use in professional reports

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I. Introduction

• Compiled programs are better for:

– Large computing projects, especially where there are multiple programmers

– Major GUI and graphics-based programs


I. Introduction




V. Scripts


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A. Abstraction

B. Algorithms

C. Programming Paradigms

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A. Abstraction

Abstraction ≡ expressing a “quality” apart from a “particular implementation.”

Example: “Exacto, maroon, Standup stapler”

or “stapler”

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Programming Language Background

A. Abstraction

• Two types for computer programming:

1. data abstraction• To convert from degrees Celsius to Kelvin, you add

273 to the temperature.

• Specific is 33°C, 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

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B. 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,

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B. Algorithms• Algorithms & abstraction in problem-solving

1. Method: Divide entire problem into subproblems. • Solutions to subproblems are algorithms. • Process of solving and assembling subproblems intosolution for entire problem is also an alogorithm of higherabstraction.

2. 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.

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C. 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.

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II. Programming Language BackgroundC. Programming Paradigms

– Three different types of paradigms:1. Functional Programming

2. Procedural Programming

3. 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

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C. Programming Paradigms1. 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

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C. Programming Paradigms2. 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

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C. Programming Paradigms3. 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 won’t need to use them!

• Languages: C++, Ada, and Java


I. Programming Language Background

II. Basic Data Manipulation

III. The MATLAB User Interface

IV.Scripts

V. Engineering Example

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A. Starting and Stopping MATLAB

B. Assigning Values to Variables

C. Data Typing

D. Classes and Objects

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Basic Data ManipulationA. 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)

• PC’s?


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MATLAB Screen

Note the double cursor to the left sideof the command window


• 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!

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III. Basic Data ManipulationB. Assigning values to Variables

– Point of confusion: MATLAB’s syntax for assigning values to variables looks like an algebra equation. It’s 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.

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B. Assigning values to Variables– Example: z = x+ y

– Note: True only for this statement.

– Programmer might change this in the next instruction: z = 4*x – y

– Some programs (Pascal and Ada) use the := to denote the difference

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Basic Data ManipulationB. 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

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B. 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 (100’s of characters!)

First 64 characters must be unique

Hyphens not allowed: file-size (no) file_size (yes)

III. Basic Data ManipulationB. Assigning Values to Variables

“Style Points”Choose names that describe variable’s content

Example: for the velocity of an object, not just “v:” velocity_in_feet_per_second or VelocityInFeetPerSecond

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III. Basic Data ManipulationC. 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.

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III. Basic Data ManipulationC. Data Typing

• Data types:

char (assign by single quotes around characters)

numeric (numbers)

• MATLAB may handle different data types the same way…

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>> radius = 49radius = 49>> radius + 1ans = 50>> radius = 'radius of a circle’radius =radius of a circle>> radius + 1ans = Columns 1 through 12 115 98 101 106 …

C. Data Typing Exer 2.3: Performing basic mathematical operations

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 dataradius 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

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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

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III. Basic Data ManipulationD. Classes and Objects

• Variables have two attributes Value - determined by what is assigned Data type (class) - the type of data stored

Example: myShoeSize = 9.5MATLAB 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.


I. Introduction




V. Scripts


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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

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IV. The MATLAB User Interface

Close icon Current directory

Workspace Window

Command window

Command historyMacintosh Display

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V. The MATLAB User InterfaceMATLAB 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

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V. The MATLAB User Interface• Command Window

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

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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

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V. The MATLAB User Interface• Command History Window

– Exercise 2.5: Using the Command History Window

– Smith text, p. 28t

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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

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V. The MATLAB User Interface

• Workspace Window and VariablesExercise 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

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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

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• 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

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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 theCurrent directory windowis. Your eye skips right over it.

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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.

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• Variable Editor– Exercise 2.12: Creating a two-dimensional matrix,

p. 33t

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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

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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

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The MATLAB User Interface• Graphics Window

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V. The MATLAB User Interface• Editor Window

– The text editor for MATLAB– Create or modify text files here– Opened by choosing File > New > 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– >> edit <file_name> in the command window


I. Introduction




V. Scripts


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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

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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

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VI. Scripts• Creating Scripts

See line by line descriptionof this simple MATLABprogram on page 36 of theSmith text.

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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

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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 > 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

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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


I. Introduction




V. Scripts


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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?

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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

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VI. Engineering Example: Spacecraft Launch• Part 1 – converting units to the metric system• 1 inch = 2.54 cm• We have: meters meters cm inch

* *foot cm inch foot

meters0.01*2.54*12

foot

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VI. Engineering Example: Spacecraft Launch• MATLAB code for converting units to the metric

system

Note line by linedescription of codeon pages 41-42 oftext.

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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

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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:

2 2

2

2

2

2

0 2

0 2

2

2 final equation

v u as

u as a g

u gs

gs u

u gs

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VI. Engineering Example: Spacecraft Launch• Complete MATLAB code for solving for the

equation

Note line by linedescription of codeon pages 41-43 oftext.

Documents

Covenant College October 7, 20151 Laura Broussard, Ph.D. Professor COS 131: Computing for Engineers Ch. 2: Getting Started with MATLAB