Introduction To Matlab Class 1

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Introduction To MatlabClass 1

• Instructors Hristiyan (Chris) Kourtev
• and Xiaotao Su, PhD
• Double click the matlab icon
• When prompted click Skip, then type
• mkdir C/MatlabClass/YourLastName
• cd C/MatlabClass/YourLastName

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Introduction

• Ask Questions!
• Slides, notes, assignments, and other info will
  be at
• http//ruccs.rutgers.edu/matlab_course/

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Setup

• Click Matlab
• mkdir C/MatlabClass/YourLastName
• cd C/MatlabClass/YourLastName

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Programming

• Matlab has its own programming language
• What is a program?
• A series of instructions that the computer
  follows
• Also referred to as Code or a Script

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Two Options For Where To Issue Commands/Instructio
ns

• In the command window
• In a script (program) executed by the command
  window.

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Hello World

• At the command prompt type
• my_var hello world
• And press ENTER.

Note The _ character is the shifted
dashSHIFT -
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Hello World

• my_var hello world

Semi-colon is so you dontoutput the result to
the screen.
Single quotes denote character string
Variable Name
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Variables
num_oranges 3.5

• my_var hello world

num_apples 7
7
hello world
3.5
my_var
num_apples
num_oranges
Variable Name
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Memory
Your computers memory

• Each of the values are stored in memory
  associated with the variable name
• The who command will list the current variables
  in memory
• Typing my_var will return the value of that
  variable

Var Name Value
my_var hello world
num_apples 7
num_oranges 3.5
subject_name john smith



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Setting values

• As you have seen you set the value of a variable
  with the sign
• You can also set a variable equal to another
  variable or the output of an operation on a
  variable.

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Setting values
new_var my_var
third_character my_var(3)
this is 7
this is 3.5
fruit num_apples num_oranges
this is now 10.5
num_apples 6
what is the value of fruit now?
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Changing around strings
my_var is currentlyhello world

• Typing my_var(3) will return l
• my_var(3) my_var(1)
• Now what is the value of my_var?

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Calling Functions

• A function is a program that you call on to do
  some sort of action
• length(hello world)
• length(my_var)
• disp(my_var)

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Nesting Functions

• disp(length(my_var))

What happens here?
disp( length(hello world) )
disp(11)
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Your first program

• What is pseudo-code and why we need it
• Typing commands one at a time isnt very
  efficient, especially when you want to do the
  same ones repeatedly
• so we create a program to do it
• This program will be called mix_strings

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Comments

• Comments are descriptions of what is happening in
  your code.
• They are need to follow what is happening for
  debugging purposes
• At the beginning of a script you put in a type of
  comment called a header

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symbol makes this line commented out This
means that the computer will ignore these lines
These lines arent for the computer, they are for
you

• mix_strings.m
• Displays the string hello world
• Then scrambles letters in that string and
• displays the scrambled string
• written by XYZ 3/6/2005

Name of file
Description What does this file do?
Who wrote it and when?
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So what is the header good for?

• Save the file
• At the command line type
• help mix_strings
• All matlab programs have headers. Find out
  information on disp, pause, and length

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What else?

• lookfor can be used to search for programs that
  have certain words in their headers.
• lookfor string
• lookfor random

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Back to the program

• clear all
• my_var hello world
• mixstr my_var
• mixstr(3) my_var(1)
• mixstr(1) my_var(3)
• disp(mixstr)

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Now run it

• In the command window
• mix_strings

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loops

• Used to repeat the same chunk of code many times
• for i15
• disp(i)
• end

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mix_strings2.m

• clear all
• my_var hello world
• mixstr xxxxxxxxxx
• for i1length(my_var)
• mixstr(i) my_var(i)
• end
• disp(mixstr)

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rand and ceil

• rand will create a random number from 0 to 1
• ceil will round up any number to the next integer
• Together you can create random integersceil(rand
  7)

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task 1

• Replace each x in mixstr with a random character
  from my_var.
• Start with the first x, then the second x
• hello world
• xxxxxxxxxxxxx
• Result could be -gt wdolhrdlhlwe

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• mix_strings3.m
• Displays the string 'hello world, then
  scrambles letters in that string
• and displays the scrambled string
• written by Chris Kourtev 7/12/2010
• clear all
• my_var 'hello world'
• mixstr 'xxxxxxxxxxxxx'
• disp(my_var)
• for i 1length(mixstr)
• mixstr(i) my_var(ceil(randlength(my_var)))
  
• end
• disp(mixstr)

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Vectors Matrixes

• A string is a list of characters
• You can also have lists of numbers using vectors
  and matrixes
• vect 1, 2, 5, 6, 3
• mat 1, 5, 3 2, 1, 5 7, 9, 0

mat 1, 5, 3 2, 1, 5 7,
9, 0
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Vectors Matrixes

• vect 1, 2, 5, 6, 3
• mat 1, 5, 3 2, 1, 5 7, 9, 0

mat 1, 5, 3 2, 1, 5 7,
9, 0
1 2 5 6 3
Vect
mat
1 5 3
2 1 5
7 9 0
note vectors are basically 1 dimensional matrixes
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Getting Values out of Vectors Matrixes
Vect
1 2 5 6 3
vect(3) returns 5
mat
1 5 3
2 1 5
7 9 0
mat(3,1) returns 7
Note to get a cell you use (ROW, COLUMN)
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vector as a 1D matrix

• vect 1
• 2
• 3
• vect2 vect

1
2
3
1 2 3
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transposing mat
mat
1 5 3
2 1 5
7 9 0
if you set t_mat mat t_mat(3, 1) is equal to
mat(1,3) Rows and columns are swapped when you
transpose a matrix
mat
1 2 7
5 1 9
3 5 0
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performing operations

• vect 3
• vect vect
• vect - 3
• vect 5, 4, 3
• matmat

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multiply and divide

• Dont forget to put a dot before multiplication
  and division symbols
• vect.3
• mat.0.5
• vect./2
• vect2 2 2 4
• vect.vect2
• vect./vect2

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task 2

• Create a 6(rows)x4(columns) matrix filled with
  random integer values between 1 and 20
• Create a zeroes matrix of the same dimensions
• Replace each zero with a random number from the
  other matrix (as we did in the mix_strings
  program)
• Display each value in the new mixed matrix
• Hint 1 You will need to use nested loops
• Hint 2 Look up how to use the zeros command
• Advanced task Design your program so that it
  can work with matrices of any dimension just by
  changing the number of rows and column. Hint
  Look up the size command