1. EGR 115 Introduction to Computing for Engineers
MATLAB Basics 2: Sub-Arrays
Lecture 5
EGR 115 Introduction to Computing for Engineers

2. EGR 115 Introduction to Computing for Engineers
Lecture Outline
MATLAB Basics
Sub-Arrays
Displaying data
Lecture 5
EGR 115 Introduction to Computing for Engineers

3. MATLAB basics Sub-arrays:
A sub-array is a subset of a larger array
>> a = [ ];
The sub-array a(2:4) is the array [3 8 5]
i.e., elements a(1,2), a(1,3), and a(1,4)
Or elements a(2), a(3), and a(4)
The sub-array a(2:2:5) is the array [3 5]
i.e., elements a(1,2) and a(1,4)
Since the array 2:2:5 is 2, 4
2:4 is the same as 2:1:4
What is the array a(1:3:9)?
Answer: a(1), a(4), a(7) ERROR!!!
Lecture 5
EGR 115 Introduction to Computing for Engineers

4. MATLAB basics Sub-arrays:
Considering 2D arrays
>> M = [ ; ; ];
The sub-array M(:,3:5) corresponds to all rows and cols 3, 4, 5
We can also index from the “end”
>> M(:,end) refers to the last column
We can reassign a sub-set of the array
>> M(1:2, [3 4]) = zeros(2,2);
An error will occur if the LHS & RHS sizes are different!!
Lecture 5
EGR 115 Introduction to Computing for Engineers

5. MATLAB basics Sub-arrays:
Some special predefined values
pi  … to 15 significant digits
1i  The square root of -1 i.e., an imaginary number
Inf  Result of dividing by zero, i.e. infinity
NaN  Not-a-Number (undefined result)
clock  date & time = [year, month, date, hr, min, sec.sec]
eps  smallest possible number in MATLAB
Machine dependent
ans  stores the result of the last calculation
Lecture 5
EGR 115 Introduction to Computing for Engineers

6. MATLAB basics Sub-arrays:
Quiz 2.2 on page 44 of textbook
c(2,:)
c(:, end)
c(1:2, 2:end)
c(6)
c(4:end)
c(1:2, 2:4)
c([1 3], 2)
c([2 2], [3 3])
What is the size of each?
Lecture 5
EGR 115 Introduction to Computing for Engineers

7. MATLAB basics Displaying Data: Display format
Setting the Default Display Format -> Preferences
Or type in command window >> format …
format_examples.m
Lecture 5
EGR 115 Introduction to Computing for Engineers

8. MATLAB basics Displaying Data: The “disp” and “fprint” functions
Using the “disp” function
>> disp(pi)
>> disp(['The value of pi = ', num2str(pi)])
The “fprintf” function (borrowed from the C-language)
Typical use: fprintf(format_spec, variable_list)
3.1416
Format (conversion char)
Description %d
Decimal notation %e
Exponential notation %f
Fixed-point notation %g
More compact notation (%f or %e) \n
New line
Lecture 5
EGR 115 Introduction to Computing for Engineers

9. MATLAB basics Displaying Data: The “fprint” function
fprintf examples:
Compare effects of the various conversion chars
>> fprintf('Compare: pi = %d pi = %e pi = %f pi = %g\n', pi, pi, pi, pi);
We can also control the field width and precision
Field width is the min number of characters to be printed
Precision is the number of decimal places
>> fprintf('Compare: pi = %5.0f pi = %5.3f pi %5.8f \n', pi, pi, pi);
fprintf in MATLAB is NOT exactly the same as the original C-function!!
Lecture 5
EGR 115 Introduction to Computing for Engineers

10. EGR 115 Introduction to Computing for Engineers
Next Lecture
Data files,
Array Operations, and
Some of the built in functions
Lecture 5
EGR 115 Introduction to Computing for Engineers