Lecture 3 Matlab Introduction

1
Lecture 3 - Matlab Introduction

• CVEN 302
• August 31, 2001

2
Lecture Goals

• Data Files
• Matlab files
• ASCII
• Matlab files
• Matlab controls

3
Matlab commands for file management

• The files can be written as a script, which
  can be loaded into the memory. From the command
  line
• echo - causes the file to be echoed to the
  screen.
• what - shows the type of file in the current
  directory.
• type - will present show the file contents

4
Matlab Files

• There are three types of files
• Data files
• Matlab files have their own format for saving
  data
• ascii files are standard text files, which can
  be printed out or used in excel files.
• m-files represent the program files.
• function files are functions similar to sin(x),
  cos(x), etc.

5
Data Files

• Data files can be written in two forms
• Matlab format
• ascii format

6
Matlab data format

• MatLab generates a data
• file, which will have
• look like
• filename.mat
• File can be loaded into
• the memory with
• load filename

• t linspace(0,2pi,40)
• x cos(t)
• save data1 t x
• clear
• whos
• what
• data1.mat
• load data1
• whos

7
ACSII format

• An ascii file type can be
• created by adding a flag
• on the end of the save
• command
• save filename.dat -ascii

• t linspace(0,2pi,30)
• x sin(t)
• save data2.dat t x -ascii
• dir
• data2.dat
• clear
• load data2.dat -ascii

8
Loading Data Files

• Matlab Files
• load filename
• The file will load the file into
• the same format as it was
• saved.

• ASCII Files
• load filename.dat -ascii
• The file will be loaded as an
• data array and will require
• you to modify to obtained the
• data vectors.

9
Data file example

• tlinspace(0,2pi,20)
• y1 sin(x)
• save data1 t y1
• clear
• (created data1.mat and
• will show up in home
• directory.)
• load data1

• (data1 will have created
• t and y1 vectors.)
• save data2.dat t y1 -ascii
• clear
• (created a ascii file with
• the data)
• load data2.dat -ascii

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Data file example continued

• (loaded an ascii file into
• memory as data2 array)
• whos
• data2 2X100 double array
• t data2(1,)
• y1 data2(2,)
• assigns the row to the vector.

• NOTE that the ascii
• file does not separate the
• vectors.

11
M-files

• These files load constants lists and executable
• programs into memory. For example
• dir
• myCon.m
• type myCon
• myCon or load myCon

12
Function M-files

• These files are similar to subroutines and will
• act as built-in functions, i.e. a tool box
  similar
• to functions, sin(x), log(x)
• Open a new m-file - Go to the top of Matlab and
  open a m-file.

13
Function files

• Function name(input variables)
• function statements
• There are set of example files show be in the
  working directory.
• twosum(x,y)
• addmult(x,y)

14
Function m-files

• The functions act similar to any of the built-in
  functions, sin(x), ln(x), etc. The inputs and
  outputs of the functions can be a variable,
  vector and/or a matrix.

15
Input functions in m-files

• Input function allows a program to input data
  into memory. The function is defined as
• variable input( string request )
• Example inputAbuse.m file

16
Output functions in m-files

• Output function allows a program to output data
  to screen. The function is defined as
• fprintf( g\n,variable)
• g is a definition of type of variable
• \n causes a carriage return.

17
Flow controls

• There are three types of flow control devices.
• Relational Operations
• Arithmetic Operations
• Logistic Operations

18
Relational Operations

• Relational operations are
• used for comparison of
• different values and
• generate a true/false
• result.

• lt less than
• lt less than or equal
• gt greater than
• gt greater than or
• equal
• equal to
• not equal

19
Logistic Operations

• Logistic operations are
• used to combine relational
• operations to generate a
• true/false result.

• and
• or
• not

20
Relational and Logistic Operations

• Try the follow set of examples type out the
  logistic
• operations. The starts a comment until you
  hit a
• return. Example
• a2 b4
• Relational Operations
• aisSmaller altb results in aisSmaller 1
  (true)
• bisSmaller blta results in bisSmaller 0
  (false)
• Logistic Operations
• bothTrue aisSmaller bisSmaller bothTrue 0
  (false)
• eithTrue aisSmaller bisSmaller eithTrue 1
  (true)
• eithTrue 0 (false)

21
Operational Precedence

• Operational precedence means the hierarchy of the
  operators
• 1 Arithmetic Operations
• 2 Relationship Operations
• 3 Logical Operations

22
Operational Precedence example

• Arithmetic Operations
• x 2 32/4 is
• x 2 ( 32 / 4 ) not x 2 3(2/4)
• So for Operational precedence
• y 3 gt 8-3 sqrt(15) gt 4
• y 3 gt 5 3.873 gt 4 arithmetic operations
• y 0 0 relational operations
• y 0 logistic

23
Program flow controls

• These commands control flow of the program.
• if else end statements
• switch structure
• for structure
• while statements

24
if flow control

• The if command can be
• used to control the flow
• of the program. There
• are three basic forms of
• the if controls.

• if (relation expression)
• block of statements
• end
• Look at the m-file see
• what it does.
• example cond1.m

25
if flow control

• The if command can
• be used with an else
• command.

• if (relation expression)
• block of statements
• else(relation expression)
• block of statements
• end
• example cond2.m and
• cond3.m

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switch flow control

• switch(relation expression)
• case 1(value)
• block of statements
• case 2(value)
• block of statements
• case 3 (value)
• block of statements
• otherwise
• end
• example cond4.m

• The switch command
• can be used for multiple
• case of the if command.

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for flow control

• for(index )
• block of statements
• end
• Type out the commands and
• see what it does.
• example
• x4,5,6,7 sumx0
• for k 1length(x)
• sumx sumx x(k)
• end

• The for command is
• used to do a series of
• steps of redundant
• process.

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for flow control

• example
• (counter) startstepfinal
• value size value
• Try n10 find out what the
• counter do.
• k 12n (1,3,5,n)
• m 0pi/15pi (0,pi/15,,pi)
• k n -11 (n,n-1,,1)

• The for command can
• have various forms of
• step sizes.

29
while flow control

• while(expression)
• block statements
• end
• Try running the example in.
• Example
• x4
• while (x-1)gt 0.01
• x sqrt(x)
• disp(x)
• end

• The while command
• can do redundant process
• by checking on a logical
• or relational operation or
• combination of the two.

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Escape commands

• break is an escape from a loop, which will go
  the end of the loop and start the next step in
  the program.
• return is an escape from a program or
  subroutine or a function and return to the main
  program.

31
Misc. Functions

• disp(expression) - displaces the expression to
  the screen.
• format (long,e,short, ...) determines the format
  of numerical values.
• global variable makes a variable available in
  any function or program as shared memory.

32
Input

• Function definition
• Summary is what the program does.
• Synopsis run program
• Input definition of terms
• Output what type of output
• Notes

33
Debugging

• Searching for and removing bugs is an inevitable
  part of programming. Bugs are caused by a number
  of factors from outright programming blunders to
  the improper application of numerical method.

34
Debugging Tools

• type and dbtype commands
• type prints out the file error
• dbtype will print out the file with line
  numbers. dbtype startstop will print out
  lines from start to stop.
• Error function - error(message) will print out
  the message and halt execution.

35
Debugging Tools

• pause command temporarily suspends the
  execution of the m-file. Useful way to print a
  warning message without necessarily aborting an
  analysis.
• keyboard command keyboard command suspends
  execution of an m-file and gives control to user.
  It gives the user access to internal variables
  of the function containing command.

36
Debug example

• The example program
• keyboard stops a program to check internal
• variables. It is a powerful tool.
• Kgtgt is the prompt and you can use it to check
  numbers out.
• Kgtgt return will return to the executable
  program.

37
Homework

• Check the Homework webpage.
• You will be writing a simple program to generate
  a set of points and generate a plot.