Matlab

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Matlab
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Textbooks

• Required Introduction to MATLAB 7 for Engineers,
  by Palm.

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Purchasing MATLAB Software

• Mathworks web site (http//www.mathworks.com).
• UH Bookstorebe sure to get version 2007
• UH-IT Department

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Purchasing MATLAB Software

• Mathworks web site (http//www.mathworks.com/prod
  ucts/matlab/). The cost is 99, plus shipping.
• IT Department ? (student) 94
• http//www.uh.edu/infotech/php/template.php?softwa
  re_id30

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Learning to use MATLAB Software

• It is strongly recommended that you perform the
  labs for the MATLAB software.
• These are Labs 7 through 12. They are available
  from the course web site.
• The schedule is also available on the website.
  Try not to fall behind.

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About MATLAB
MATLAB is

• a computer programming language
• a software environment for using the language
  effectively

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Two modes of operation
About MATLAB

• Interactive calculator mode
• Script mode execution of complete programs ?
  script files

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About MATLAB

• Running MATLAB creates one or more windows
• One is called the MATLAB Desktop Primary
  graphical user interface for MATLAB
• Contains and manages all other windows that are
  part of MATLAB
• According to the configuration some windows may
  be visible and some may not. You can see this
  information in the View Menu

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About MATLAB Desktop
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About MATLAB Desktop

• MATLAB Desktop Windows
• Command Window Primary place to interact with
  MATLAB. Place where the user issues the commands.
  The MATLAB command prompt is the symbol gtgt
• Command History Running history of prior
  commands issued in the Command Window.

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About MATLAB Desktop

• MATLAB Desktop Windows
• Workspace GUI for viewing, loading, and saving
  MATLAB variables.
• Launch Pad Tree layout for access to tools,
  demos and documentation
• Current Directory GUI for directory and file
  manipulation in MATLAB.

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About MATLAB Desktop

• MATLAB Desktop Windows
• Help GUI for finding and viewing on-line
  documentation.
• Array Editor GUI for modifying the content of
  MATLAB variables
• Editor/Debugger Text editor and debugger for
  MATLAB text files.

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What does Matlab understand?

• Real numbers 1 -14 7.65432 2e3
• Complex numbers 23i 4-6j 2i
• Arrays of numbers 1,2,3 1,23,4
• Strings I wish I knew that!

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MATLAB Take 1 Basics
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Basics Basic Operations
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Basics Rules of Precedence
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Basics Rules of Precedence

• precedence examples
• 8 3 5
• (8 (3 5)) 23
• 4 2 12 8 / 4 2
• ((4 2) 12 ((8 / 4) 2))) 0
• 3 4 2 5
• ((3 (4 2)) 5) 53
• 27 1 / 3 32 0.2
• (((27 1) / 3 ) (32 0.2))11

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Basics Variables

• Variable is a symbol used to contain a value
• MATLAB has some rules to name variables
• Variables names are case sensitive
• BOB, Bob, bob, BoB ? all different!
• Variables names can contain up to 31 characters.
  Any additional characters are ignored
• Variable names must start with a letter, followed
  by any number of letters, digits or underscores.
  Punctuation characters are not allowed, because
  most of them have a special meaning in MATLAB

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Basics Variables

• Some names cannot be used for variables for,
  end, if, while, function, return, elseif, case,
  otherwise, switch, continue, else, try, catch,
  global, persistent, break
• If you try to use any of these reserved words as
  a variable, MATLAB will report an error
• Of course, you can use words similar by
  capitalizing one or more letters
• Also, MATLAB has a number of special variables
  and constants

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Basics Special Variables and Constants
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Basics

• Assignment or replacement operator
• It works different than the equal sign the
  variable on the left-hand side is replaced by the
  value generated by the right-hand side.
  Therefore, only one variable name must be in the
  left-hand side
• x x 2
• 6 x ? NOT VALID!!!
• The right-hand side must have a computable value
• x 5 y Is y defined?

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MATLAB Take 2 Programming with MATLAB
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The Problem Solving Process - 5 Steps

• 1. Understand the problem - diagram or sketch is
  good.
• 2. Collect information - data, theories,
  assumptions, approximations.
• 3. Generate an algorithm, or maybe more than one.
• 4. Refine and implement - use a tool
  spreadsheet, MATLAB, or other computer
  program/language.
• 5. Verify and test - estimate, work another way,
  try other data input, compare with a plot, check
  dimensional consistency.

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Programming

• Example Volume of a circular cylinder
• Given a circular cylinder with height 15m and
  radius 8 m, find the radius of a cylinder of the
  same height but with a volume that is 20 larger.

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Solution Algorithm

• Calculate current volume
• Calculate desired volume
• Determine new radius by rewriting volume equation
  in terms of radius

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Basics

• Example Volume of a circular cylinder
• V ? r2 h
• h 15m
• r 8m
• Find the radius of a cylinder with volume 20
  greater, and the same height
• pie 3.1416
• r 8
• h 15
• V pier2h
• V 1.2V
• r sqrt(V/(pieh))

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Alternative Approach

• The formula for volume is V?r2h
• The radius is given by

gtgt r 8 gtgt h 15 gtgt V pir2h gtgt newV
1.2V gtgt newr sqrt(newV/(pih)) ans 8.7636
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Basics Commands
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Basics Complex Numbers

• complex number example
• s 3 7j
• w 5 9j
• MATLAB Example
• Given x -5 9j and y 6 2j
• find
• x y
• 17j
• xy
• -12 64j
• x/y
• -1.2 1.1j

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Some Simple Functions

• sin(x)
• sqrt(x)
• acos(x)
• exp(x)
• log(x)

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Interpretation

• sin(180) ?
• -0.8012
• The argument is in radians.
• acos(.5) ?
• 1.0472
• The solution is in radians.

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Interpretation

• exp(1) ?
• 2.7183
• This is e.
• log(10) ?
• 2.3026
• This is the natural log, not base 10.

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Polynomials in Matlab

• A polynomial is represented by its array of
  coefficients, beginning with the leading
  coefficient (coefficient of highest power)

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Special Polynomial Functions

• polyval(a,x) evaluates polynomial whose
  coefficients are in array a at the point x
• roots(a) returns a vector containing all of the
  roots of the polynomial whose coefficients are in
  the array a
• poly(v) returns the coefficient vector of a
  polynomial whose roots are stored in the vector v

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Polynomial Examples

• gtgt a2,4,-1,5
• gtgt polyval(a,0)
• ans
• 5
• gtgt poly(1, 2, 3)
• ans
• 1 -6 11 -6

• gtgt vroots(a)
• v
• -2.5722
• 0.2861 0.9434j
• 0.2861 - 0.9434j

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Plotting in Matlab

• The basic command to plot a set of points in the
  plane is plot(x,y)
• x is a vector containing the horizontal
  coordinates
• y is a vector containing the vertical coordinates
• x y must be the same sizeeither both row
  vectors or both column vectors
• The plot actually appears in a separate window,
  called a figure window.

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Plotting Example

• gtgt x00.0110 generate x values
• gtgt ysin(x) generate y values
• sine function
• applied to array of xs
• gtgt figure(1) give number to figure
• gtgt plot(x,y),title('My first Plot'),
• xlabel('x axis'),
• ylabel('y axis')

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Plotting in MATLAB
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Plotting in MATLAB

• Some Plot Options

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Matlab Files

• Script function filesplain ASCII, extension .m
• MAT filesbinary file, used to save workspace
  variables, extension .mat

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gtgt pi ans 3.1416 gtgt format long gtgt pi ans
3.14159265358979 gtgt format rat gtgt pi ans
355/113
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Controlling Input and Output

• The disp Function Useful to control the output
• disp Display array.
• disp(X) displays the array, without printing the
  array name. It's the same as leaving the
  semicolon off an expression except that empty
  arrays don't display. If X is a string, the text
  is displayed.
• EXAMPLES
• gtgt disp(X) displays the value of variable X, but
  not its name
• gtgt disp(The value of X is) displays the
  string The value of X isbut no number

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Controlling Input and Output

• The num2str Function Useful to make the output
  look better
• num2str Convert number to string.
• Tnum2str(X) converts the array X into a
  string representation T with about 4 digits and
  an exponent if required. Allows display of label
  on same line as value.
• gtgt x3.24567
• gtgt disp('The value of x is ',num2str(x),'ft')
• The value of x is 3.2457ft

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Controlling Input and Output

• The input Function Used to get interactive
  input.
• input Prompt for user input.
• R input('How many apples') gives the user
  the prompt in the text string and waits for input
  from the keyboard. The input can be any MATLAB
  expression, which is evaluated, using the
  variables in the current workspace, and the
  result returned in R. If the user presses the
  return key without entering anything, INPUT
  returns an empty matrix.
• R input('What is your name','s') gives the
  prompt in the text string and waits for character
  string input. The typed input is not evaluated
  the characters are simply returned as a MATLAB
  string.

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Controlling Input and Output

• The Menu Function Used to get interactive input
  by selection of an alternative from a menu.
• k menu(title,option1,option2,)
• choices'B','D','F'
• kmenu('Whodoyouwant?',choices(1),choices(2),choic
  es(3))
• disp('You picked ',choices(k))

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Input from File

• load as a command or as a function, requires
  each line in file has same number of values,
  loads entire contents of file into an array
• gtgtload data.txt name of array will be data
• gtgtload(new.txt) name of array will be new
• gtgtmydata load(proj3.txt) name of array
  will be mydata