1. EGR 115 Introduction to Computing for Engineers
MATLAB Basics 1: Variables & Arrays
Lecture 4
EGR 115 Introduction to Computing for Engineers

2. EGR 115 Introduction to Computing for Engineers
Lecture Outline
MATLAB Basics
Variables and arrays
Lecture 4
EGR 115 Introduction to Computing for Engineers

3. MATLAB basics Variables and arrays:
A variable is a symbolic name (or identifier) which serves as a placeholder or container for “data”
It is good programming practice to use a pertinent name for variables
E.g., >> accel_due_to_gravity = 9.81; % g in m/s^2
Variables exhibit a variety of properties
Scope or visibility
Is it globally or only locally visible?
Extent
Life-time of the variable?
Type
Is it an integer, float, character, …
Lecture 4
EGR 115 Introduction to Computing for Engineers

4. MATLAB basics Variables and arrays:
Strongly typed languages
Requires that the data type of the variable must be declared before it is used
E.g., int miles;
The variable “miles” is declared to be of type integer
Weakly typed languages
Does NOT Requires that the data type of the variable be declared before it is used
E.g., >> letters = ‘ab’;
The variable “letters” is determined to be of type character because of the type of data assigned to the variable.
C programming language
MATLAB programming language
Lecture 4
EGR 115 Introduction to Computing for Engineers

5. MATLAB basics Variables and arrays – Matrices (2D arrays)
An array is a multi-dimensional list
A matrix is a 2-dimensional array with rows and columns
E.g., the game Sudoku
Lecture 4
EGR 115 Introduction to Computing for Engineers

6. MATLAB basics Variables and arrays – Matrices (2D arrays)
column 1
column 2
column 3
column 4
column 5
M ( row , column )
row 1 ?
row 2
row 3
row 4
What is the address of the element in question?
Answer: M( 2 , 4 )
What is the size of the matrix?
Answer: It is a 4 X 5 matrix
Lecture 4
EGR 115 Introduction to Computing for Engineers

7. MATLAB basics Variables and arrays – Vectors (1D arrays)
A vector is a one-dimensional array
It could be a row vector
Or, it could be a column vector
A scalar is an array with only a single element
E.g., a 1X1 matrix or a vector with only one entry
Lecture 4
EGR 115 Introduction to Computing for Engineers

8. EGR 115 Introduction to Computing for Engineers
MATLAB basics Variables and arrays: Matrix, Vector, and scalar examples
Examples
‘a’ is a 32 array or 32 matrix
‘b’ is a 14 array or 4-element row vector
‘c’ is a 31 array or 3-element column vector
‘d’ is a scalar (or 11 array)
Lecture 4
EGR 115 Introduction to Computing for Engineers

9. MATLAB basics Variables and arrays – Data types
MATLAB data types:
The default data type in MATLAB is double
i.e., 64-bit floating point type number
E.g., >> var = 22;
Imaginary numbers are distinguished by ‘i’, or ‘j’
E.g., >> var = 11.2i;
Variables of type character (requires single quotes)
E.g., >> comment = ‘Please Help Me’;
Actually, a 114 character array!!
MATLAB stores var as a double precision float
Lecture 4
EGR 115 Introduction to Computing for Engineers

10. MATLAB basics Variables and arrays - Initialization
In MATLAB variables are automatically created when they are initialized.
>> x = [ ]
Creates a 13 1-dimensional array ‘x’ (row vector) of doubles
>> x = [2.2, 1.0, 3.5]
Same as above (the commas are optional)
>> y = [2.2; 1.0; 3.5]
Creates a 31 column vector.
>> y = [ ]
Same as above
Lecture 4
EGR 115 Introduction to Computing for Engineers

11. MATLAB basics Variables and arrays:
Creating and initializing a matrix
>> z = [ 1 2 3; 4 5 6]
Creates a 23 array (matrix)
>> z = [ ]
Same as above (easier to read?)
>> z = [ 1, 2, 3; , 5, 6]
Same as above
>> z = []
Creates an empty array (size is undefined)
Matrix must be a rectangular (or square)
All cols the same length and
All rows the same length
Lecture 4
EGR 115 Introduction to Computing for Engineers

12. MATLAB basics Variables and arrays:
Abbreviated Initialization
X = start : increment : end
>> x = 0.5 : 1.5 : 6
Initializing with built-in functions
>> a = zeros (2, 5)
>> b = ones(1, 4)
>> c = zeros(3, 1)
>> d = ones(3, 2)
Can ask MATLAB to determine the size of an array
>> size(d)
Lecture 4
EGR 115 Introduction to Computing for Engineers

13. MATLAB basics Variables and arrays:
Initializing with keyboard input
val = input('Any text to prompt user to enter a value ');
Try it!!
MATLAB supports arrays with greater than two dimensions
We will rarely go beyond 2D arrays (i.e., matrices)
How does MATLAB store matrices in memory?
Column major order (some Prog languages are row major)
All of 1st col, then all of 2nd col, ….
E.g., >> z = [ 1, 2, 3; , 5, 6]
e.g., C and C++ are row major!!
What is the value of z(3)?
Answer: z(3) = z(1,2) = 2
Lecture 4
EGR 115 Introduction to Computing for Engineers

14. EGR 115 Introduction to Computing for Engineers
Next Lecture
Sub-Arrays
Displaying data
Lecture 4
EGR 115 Introduction to Computing for Engineers