MATLAB Cookbook – Code Examples for the Most Common Tasks

cover_matlab_cookbook

In this post, I will write example code for the most common things you’ll do in MATLAB. MATLAB is a software package used for numerical computation and visualization.

My goal is to write bare-bones, skeleton recipes that can be easily modified and adapted to your own projects.


Prerequisites

  • You have MATLAB installed on your computer. I’m using MATLAB Release 2020a.

Select a Current Directory

Open MATLAB.

In the command window, select your desired Current Folder (i.e. working directory). The syntax is:

cd 'path_to_folder'

For example., in the Command Window, you would type the following command and press Enter in your keyboard:

cd 'C:\Program Files\My_Documents'

Create New Scripts

To create a new script (i.e. the most basic Matlab file with the ‘.m’ extension), run the following command in the Command window.

edit matlab_cookbook_1.m

If this is your first time creating a file in MATLAB, you might see a prompt that asks you “Do you want to create it?”

Highlight “Do not show this prompt again,” and click Yes.

Accept User Input

Write the following code inside matlab_cookbook_1.m.

% Get rid of blank lines in the output
format compact

% Accept a string as input
% Semicolon prevents every variable and output from appearing
% in the command window
name = input("What's your first name : ", "s");

% Check if the user entered something as input
if ~isempty(name)
    fprintf("Hi %s\n", name) 
end

Save the code.

Click Run to run the code.

Type in your name into the Command Window.

Press Enter.

Here is the output:

2-user-input-output

To stop a script from running at any time, you can type CTRL+C.

Now, let’s create a new file named matlab_cookbook_2.m.

edit matlab_cookbook_2.m

Add the following code:

% Get rid of blank lines in the output
format compact

% Accept vector input
vector_input = input("Enter a vector : ");

% Display the vector to the Command Window
disp(vector_input)

Click Run.

Enter your vector. For example, you can enter:

[1 2 3]

Here is the output:

3-enter-your-vector

Declare and Initialize Variables and Data Types

Let’s work with variables and data types (i.e. classes).

Create a new script.

edit matlab_cookbook_3.m

Type the following code.

format compact

% Initialize a character variable
char_1 = 'A'

% Determine the class of a character
class(char_1)

% Initialize a string variable
str_1 = "This is a string"

% Determine the class
class(str_1)

% Evaluate a boolean expression
5 > 2

% Initialize a boolean varable to true
bool_1 = true

% Initialize a boolean variable to false
bool_2 = false

% Check out the maximum and minimum values that can be 
% stored in a data type
intmin('int8')
intmax('int8')

% See the largest double value that can be stored
realmax

% See the largest integer that can be stored
realmax('single')

Run it.

Here is the output:

4-matlab-cookbook3-output1
4-matlab-cookbook3-output2

How do you create an expression that spans more than one line?

Open a new script.

edit matlab_cookbook_4.m
format compact

% An expression that spans more than one line
var_1 = 5 + 5 + 1 ...
      + 1

Save and then run the code. 

5-matlab-cookbook4-output

Casting Variables to Different Data Types

Let’s explore how to cast variables to different data types.

Create a new script.

edit matlab_cookbook_5.m

Type the following code.

format compact

% Create a double (double is the default)
var_1 = 9

% Output the data type
class(var_1)

% Caste the double to an int8 data type
var_2 = int8(var_1)

% Check that the variable was properly converted
class(var_2)

% Convert a character to a double
var_3 = double('A')

% Convert a double to a character 
var_4 = char(64)

Run it.

Here is the output:

6-matlab-cookbook5-output

Formatting Data into a String

Let’s explore how to format data into a string.

Create a new script.

edit matlab_cookbook_6.m

Type the following code.

format compact

% Format output into a string.
% Sum should be a signed integer - %d
sprintf('9 + 2 = %d\n', 9 + 2)

% Format output into a string.
% Sum should be a float with two decimal places
sprintf('9 + 2 = %.2f\n', 9 + 2)

Run it.

Here is the output:

7-matlab-cookbook6-output

Basic Mathematical Operations

Let’s explore how to do basic mathematical operations in MATLAB.

Create a new script.

edit matlab_cookbook_7.m

Type the following code.

% Supress the display of blank lines
format compact 

% Display formatted text
% Addition
fprintf('9 + 2 = %d\n', 9 + 2)

% Subtraction
fprintf('9 - 2 = %d\n', 9 - 2)

% Multiplication
fprintf('9 * 2 = %d\n', 9 * 2)

% Display float with two decimal places
fprintf('9 * 2 = %0.2f\n', 9 / 2)

% Exponentiation
fprintf('5^2 = %d\n', 5^2)

% Modulus
fprintf('5%%2 = %d\n', mod(5,2))

% Generate a random number between 50 and 100
randi([50,100]) 

Run it.

Here is the output:

8-matlab-cookbook7-output

Basic Mathematical Functions

Let’s take a look at some basic mathematical functions in MATLAB.

Create a new script.

edit matlab_cookbook_8.m

Type the following code.

format compact

% This code has some basics mathematical functions
% in MATLAB

% Absolute Value
fprintf('abs(-7) = %d\n', abs(-7))

% Floor
fprintf('floor(3.23) = %d\n', floor(3.23))

% Ceiling
fprintf('ceil(3.23) = %d\n', ceil(3.23))

% Rounding
fprintf('round(3.23) = %d\n', round(3.23))

% Exponential (e^x)
fprintf('exp(1) = %f\n', exp(1)) 

% Logarithms
fprintf('log(100) = %f\n', log(100))
fprintf('log10(100) = %f\n', log10(100))
fprintf('log2(100) = %f\n', log2(100))

% Square root
fprintf('sqrt(144) = %f\n', sqrt(144))

% Convert from degrees to radians
fprintf('90 Deg to Radians = %f\n', deg2rad(90))

% Convert from radians to degrees
fprintf('pi/2 Radians to Degrees = %f\n', rad2deg(pi/2))

%%%% Trigonometric functions%%%
% Sine of argument in radians
fprintf('Sine of pi/2 = %f\n', sin(pi/2))

% Cosine of argument in radians
fprintf('Cosine of pi/2 = %f\n', cos(pi/2))

% Tangent of argument in radians
fprintf('Tangent of -pi/4 = %f\n', tan(-pi/4))

Run it.

Here is the output:

9-matlab-cookbook8-output

To see a big list of the built-in mathematical functions, you can type the following command:

help elfun

Relational and Logical Operators

Create a new script.

edit matlab_cookbook_9.m

Type the following code.

format compact

%{ 
Relational Operators: 
  -- Greater than >
  -- Less than < 
  -- Greater than or equal to >=
  -- Less than or equal to <=
  -- Equal to ==
  -- Not equal to ~=

Logical Operators: 
  -- OR || 
  -- AND &&
  -- NOT ~
%} 

% Example
age = 19

if age < 18
    disp("You are not in college yet")
elseif age >= 18 && age <= 22
    disp("You are a college student")
else
    disp("You have graduated from college")
end   

Run it.

Here is the output:

10-matlab-cookbook9-output

Now, let’s work with switch statements.

edit matlab_cookbook_10.m

Here is the output:

format compact

size = 12

switch size
    case 2
        disp("Too small")
    case num2cell(3:10) % If number is between 3 and 10, inclusive
        disp("Just right")
    case {11, 12, 13, 14} % If number is any of these numbers
        disp("A bit large")
    otherwise
        disp("Too big")
end  

Vectors

edit matlab_cookbook_11.m

Here is the output:

format compact

% Create a vector
vector_1 = [6 9 1 3 8]

% Calculate the length of the vector
vector_1_length = length(vector_1)

% Sort a vector in ascending order
vector_1 = sort(vector_1)

% Sort a vector in descending order
vector_1 = sort(vector_1, 'descend')

% Create a vector that has the numbers 3 through 9
vector_2 = 3:9

% Create a vector of numbers from 10 through 15 in steps of 0.5
vector_3 = 10:0.5:15

% Concatenate vectors
vector_4 = [vector_2 vector_3] 

% Get the first item in the vector above. Indices start at 1.
vector_4(1)
edit matlab_cookbook_12.m
format compact

% Create a vector
vector_1 = [6 9 1 3 8]

% Get the last value in a vector
last_val_in_vector = vector_1(end)

% Change the first value in a vector
vector_1(1) = 7

% Append values to end of vector
vector_1(6) = 99

% Get the first 3 values of a vector
vector_1(1:3)

% Get the first and second value of a vector
vector_1([1 2])

% Create a column vector
col_vector_1 = [6;9;1;3;8]

% Multiply a column vector and a row vector
vector_mult = col_vector_1 * vector_1

% Take the dot product of two vectors
% 2 * 5 + 3 * 9 + 4 * 7 = 65
vector_2 = [2 3 4]
vector_3 = [5 9 7]
dot_product_val = dot(vector_2, vector_3)

Here is the output:

13-matlab-cookbook12-output

Matrix Basics

edit matlab_cookbook_13.m
format compact

% Initialize a matrix
matrix_1 = [4 6 2; 6 3 2]

% Get the number of values in a row
num_in_a_row = length(matrix_1)

% Get the total number of values in a matrix
num_of_vals = numel(matrix_1)

% Size of matrix (num rows   num cols)
matrix_size = size(matrix_1)

[num_of_rows, num_of_cols] = size(matrix_1)

% Generate a random matrix with values between 20 and 30
% Matrix has two rows.
matrix_2 = randi([20,30],2)

% Modify a value inside a matrix (row 1, column 2)
% Remember matrices start at 1
matrix_2(1, 2) = 33

% Modify all row values in the first row
matrix_2(1,:) = 26

% Modify all column values in the first column
matrix_2(:,1) = 95

% Get the first value in the last row
first_val_last_row = matrix_2(end, 1)

% Get the second value in the last column
second_val_last_col = matrix_2(2, end)

% Delete the second column
matrix_2(:,2) = [];

Loops

For loops

edit matlab_cookbook_14.m
format compact

% Loop from 1 through 5
for i = 1:5
    disp(i) % Display
end

% Add a space
disp(' ')

% Decrement from 5 to 0 in steps of 1
for i = 5:-1:0
    disp(i)
end

% Add a space
disp(' ')

% Loop from 1 through 3
for i = [1 2 3]
    disp(i)
end

% Add a space
disp(' ')

% Create a matrix
matrix_1 = [1 4 5; 6 2 7];

% Nested for loop to run through all values in a matrix
for row = 1:2
    for col = 1:3
        disp(matrix_1(row, col))
    end
end

% Go through an entire vector
vector_1 = [2 8 3 5]
for i = 1:length(vector_1)
    disp(vector_1(i))
end

Output:

14-matlab-cookbook14-output

While loops

edit matlab_cookbook_15.m
format compact

% Create a while loop
i = 1
while i < 25
    % If the number is divisible by 5
    if(mod(i,5)) == 0
        disp(i)
        i = i + 1;
        continue
    end
    % Else
    i = i + 1;
    if i >= 14
        % Prematurely leave the while loop
        break
    end
end

Output:

15-matlabcookbook15-output

Matrix Operations

edit matlab_cookbook_16.m

Here is the first part of the output.

format compact

% Initialize a 3x3 matrix
matrix_1 = [4 6 2; 3 6 14; 5 2 9]

matrix_2 = [2:4; 7:9]
matrix_3 = [5:7; 9:11]
matrix_4 = [1:2; 3:4; 2:3]

% Add two matrices together
matrix_2 + matrix_3

% Multiply corresponding elements of two matrices together
matrix_2 .* matrix_3

% Multiply two matrices together
matrix_2 * matrix_4

% Perform the square root on every value in a matrix
sqrt(matrix_1)

% Double everything in a matrix
matrix_2 = matrix_2 * 2

% Sum everything in each column
sum(matrix_2)

% Convert a matrix to a boolean array
% Any value greater than 5 is 1
greater_than_five = matrix_1 > 5

Cell Arrays

edit matlab_cookbook_17.m
format compact

% Create a cell array
cell_array_1 = {'Automatic Addison', 25, [6 32 54]}

% Preallocate a cell array to which we will later assign data
cell_array_2 = cell(3)

% Get the first value in the cell array
cell_array_1{1}

% Add more information 
cell_array_1{4} = 'John Doe'

% Get the length of the cell array
length(cell_array_1)

% Display the values in a cell array
for i = 1:length(cell_array_1)
    disp(cell_array_1{i})
end

Here is the output:

17-matlabcookbook17-output

Strings

edit matlab_cookbook_18.m

format compact

% Initialize a string
my_string_1 = 'Automatic Addison'

% Get the length of the string
length(my_string_1)

% Get the second value in the string
my_string_1(2)

% Get the first three letters of the string
my_string_1(1:3)

% Concatenate
longer_string = strcat(my_string_1, ' We''re longer now')

% Replace a value in a string
strrep(longer_string, 'now', 'immediately')

% Split a string based on space delimiter
string_array = strsplit(longer_string, ' ')

% Convert an integer to a string
num_string = int2str(33)

% Convert a float to a string
float_string = num2str(2.4928)

Here is the output:

18-matlabcookbook18-outputJPG

Structures

Here is how to create your own custom data type using structures. Structures consist of key-value pairs (like a dictionary).

edit matlab_cookbook_19.m
format compact

automatic_addison = struct('name', 'Automatic Addison', ...
    'age', 35, 'item_purchased', [65 23])

% Get his age
disp(automatic_addison.age)

% Add a field
automatic_addison.favorite_food = 'Oatmeal'

% Remove a field
automatic_addison = rmfield(automatic_addison, 'favorite_food')

% Store a structure in a vector
clients(1) = automatic_addison

Here is the output:

19-matlabcookbook19-output

Tables

edit matlab_cookbook_20.m
format compact

name = {'Sam'; 'Bill'; 'John'};
age = [32; 52; 19];
salary = [45000; 90000; 15000]
id = {'1', '2', '3'}

% The name of each row will be the id
employees = table(name, age, salary, ...
    'RowName', id)

% Get the average salary
avg_salary = mean(employees.salary)

% 'help table' command helps you find what you can do with tables

% Add a new field
employees.vacation_days = [10; 20; 15]

Here is the output:

20-matlabcookbook20-output

File Input/Output

edit matlab_cookbook_21.m
format compact

% Generate a random 8x8 matrix
random_matrix = randi([1,5],8)

% Save the matrix as a text file
save sample_data_1.txt random_matrix -ascii

% Load the text file
load sample_data_1.txt

disp sample_data_1 

type sample_data_1.txt

Here is the output:

21-matlabcookbook21-output

Functions

edit matlab_cookbook_22.m
format compact

% Input vector
values = [9.7, 63.5, 25.2, 72.9, 1.1];

% Calculate the average and store it
mean = average(values)

% Define a function named average.m that 
% accepts an input vector and returns the average
function ave = average(x)
    % Take the sum of all elements in x and divide 
    % by the number of elements
    ave = sum(x(:))/numel(x); 
end

Here is the output:

22-matlabcookbook22-output

Creating a Plot

edit basic_plot.m
% Graph a parabola
x = [-100:5:100];
y = x.^2;
plot(x, y)

Here is the output:

23-basic-plotJPG