[ MATLAB Tutorial - Lession 3] Command

MATLAB is an interactive program for numerical computation and data visualization. You can enter a command by typing it at the MATLAB prompt '>>' on the Command Window.

In this section, we will provide lists of commonly used general MATLAB commands.

Commands for Managing a Session

MATLAB provides various commands for managing a session. The following table provides all such commands −

Command	Purpose
clc	Clears command window.
clear	Removes variables from memory.
exist	Checks for existence of file or variable.
global	Declares variables to be global.
help	Searches for a help topic.
lookfor	Searches help entries for a keyword.
quit	Stops MATLAB.
who	Lists current variables.
whos	Lists current variables (long display).

Commands for Working with the System

MATLAB provides various useful commands for working with the system, like saving the current work in the workspace as a file and loading the file later.

It also provides various commands for other system-related activities like, displaying date, listing files in the directory, displaying current directory, etc.

The following table displays some commonly used system-related commands −

Command	Purpose
cd	Changes current directory.
date	Displays current date.
delete	Deletes a file.
diary	Switches on/off diary file recording.
dir	Lists all files in current directory.
load	Loads workspace variables from a file.
path	Displays search path.
pwd	Displays current directory.
save	Saves workspace variables in a file.
type	Displays contents of a file.
what	Lists all MATLAB files in the current directory.
wklread	Reads .wk1 spreadsheet file.

Input and Output Commands

MATLAB provides the following input and output related commands −

Command	Purpose
disp	Displays contents of an array or string.
fscanf	Read formatted data from a file.
format	Controls screen-display format.
fprintf	Performs formatted writes to screen or file.
input	Displays prompts and waits for input.
;	Suppresses screen printing.

The fscanf and fprintf commands behave like C scanf and printf functions. They support the following format codes −

Format Code	Purpose
%s	Format as a string.
%d	Format as an integer.
%f	Format as a floating point value.
%e	Format as a floating point value in scientific notation.
%g	Format in the most compact form: %f or %e.
\n	Insert a new line in the output string.
\t	Insert a tab in the output string.

The format function has the following forms used for numeric display −

Format Function	Display up to
format short	Four decimal digits (default).
format long	16 decimal digits.
format short e	Five digits plus exponent.
format long e	16 digits plus exponents.
format bank	Two decimal digits.
format +	Positive, negative, or zero.
format rat	Rational approximation.
format compact	Suppresses some line feeds.
format loose	Resets to less compact display mode.

Vector, Matrix and Array Commands

The following table shows various commands used for working with arrays, matrices and vectors −

Command	Purpose
cat	Concatenates arrays.
find	Finds indices of nonzero elements.
length	Computes number of elements.
linspace	Creates regularly spaced vector.
logspace	Creates logarithmically spaced vector.
max	Returns largest element.
min	Returns smallest element.
prod	Product of each column.
reshape	Changes size.
size	Computes array size.
sort	Sorts each column.
sum	Sums each column.
eye	Creates an identity matrix.
ones	Creates an array of ones.
zeros	Creates an array of zeros.
cross	Computes matrix cross products.
dot	Computes matrix dot products.
det	Computes determinant of an array.
inv	Computes inverse of a matrix.
pinv	Computes pseudoinverse of a matrix.
rank	Computes rank of a matrix.
rref	Computes reduced row echelon form.
cell	Creates cell array.
celldisp	Displays cell array.
cellplot	Displays graphical representation of cell array.
num2cell	Converts numeric array to cell array.
deal	Matches input and output lists.
iscell	Identifies cell array.

Plotting Commands

MATLAB provides numerous commands for plotting graphs. The following table shows some of the commonly used commands for plotting −

Command	Purpose
axis	Sets axis limits.
fplot	Intelligent plotting of functions.
grid	Displays gridlines.
plot	Generates xy plot.
print	Prints plot or saves plot to a file.
title	Puts text at top of plot.
xlabel	Adds text label to x-axis.
ylabel	Adds text label to y-axis.
axes	Creates axes objects.
close	Closes the current plot.
close all	Closes all plots.
figure	Opens a new figure window.
gtext	Enables label placement by mouse.
hold	Freezes current plot.
legend	Legend placement by mouse.
refresh	Redraws current figure window.
set	Specifies properties of objects such as axes.
subplot	Creates plots in subwindows.
text	Places string in figure.
bar	Creates bar chart.
loglog	Creates log-log plot.
polar	Creates polar plot.
semilogx	Creates semilog plot. (logarithmic abscissa).
semilogy	Creates semilog plot. (logarithmic ordinate).
stairs	Creates stairs plot.
stem	Creates stem plot.

[ Matlab Tutorial - Lession 2] Variables

In MATLAB environment, every variable is an array or matrix.

You can assign variables in a simple way. For example,

 Live Demo

x = 3        % defining x and initializing it with a value

MATLAB will execute the above statement and return the following result −

x = 3

It creates a 1-by-1 matrix named x and stores the value 3 in its element. Let us check another example,

 Live Demo

x = sqrt(16)  % defining x and initializing it with an expression

MATLAB will execute the above statement and return the following result −

x = 4

Please note that −

• Once a variable is entered into the system, you can refer to it later.
• Variables must have values before they are used.
• When an expression returns a result that is not assigned to any variable, the system assigns it to a variable named ans, which can be used later.

For example,

 Live Demo

sqrt(78)

MATLAB will execute the above statement and return the following result −

ans =  8.8318

You can use this variable ans −

 Live Demo

sqrt(78);
9876/ans

MATLAB will execute the above statement and return the following result −

ans =  1118.2

Let's look at another example −

 Live Demo

x = 7 * 8;
y = x * 7.89

MATLAB will execute the above statement and return the following result −

y =  441.84

Multiple Assignments

You can have multiple assignments on the same line. For example,

 Live Demo

a = 2; b = 7; c = a * b

MATLAB will execute the above statement and return the following result −

c = 14

I have forgotten the Variables!

The who command displays all the variable names you have used.

who

MATLAB will execute the above statement and return the following result −

Your variables are:
a    ans  b    c   

The whos command displays little more about the variables −

• Variables currently in memory
• Type of each variables
• Memory allocated to each variable
• Whether they are complex variables or not

whos

MATLAB will execute the above statement and return the following result −

Attr Name        Size        Bytes      Class
==== ====        ====        ====       ===== 
   a             1x1           8        double
   ans           1x70         757        cell
   b             1x1           8        double
   c             1x1           8        double

Total is 73 elements using 781 bytes     

The clear command deletes all (or the specified) variable(s) from the memory.

clear x     % it will delete x, won't display anything
clear       % it will delete all variables in the workspace
            %  peacefully and unobtrusively 

Long Assignments

Long assignments can be extended to another line by using an ellipses (...). For example,

 Live Demo

initial_velocity = 0;
acceleration = 9.8;
time = 20;
final_velocity = initial_velocity + acceleration * time

MATLAB will execute the above statement and return the following result −

final_velocity = 196

The format Command

By default, MATLAB displays numbers with four decimal place values. This is known as short format.

However, if you want more precision, you need to use the format command.

The format long command displays 16 digits after decimal.

For example −

 Live Demo

format long
x = 7 + 10/3 + 5 ^ 1.2

MATLAB will execute the above statement and return the following result−

x = 17.2319816406394

Another example,

 Live Demo

format short
x = 7 + 10/3 + 5 ^ 1.2

MATLAB will execute the above statement and return the following result −

x = 17.232

The format bank command rounds numbers to two decimal places. For example,

 Live Demo

format bank
daily_wage = 177.45;
weekly_wage = daily_wage * 6

MATLAB will execute the above statement and return the following result −

weekly_wage = 1064.70

MATLAB displays large numbers using exponential notation.

The format short e command allows displaying in exponential form with four decimal places plus the exponent.

For example,

 Live Demo

format short e
4.678 * 4.9

MATLAB will execute the above statement and return the following result −

ans = 2.2922e+01

The format long e command allows displaying in exponential form with four decimal places plus the exponent. For example,

 Live Demo

format long e
x = pi

MATLAB will execute the above statement and return the following result −

x = 3.141592653589793e+00

The format rat command gives the closest rational expression resulting from a calculation. For example,

 Live Demo

format rat
4.678 * 4.9

MATLAB will execute the above statement and return the following result −

ans = 34177/1491 

Creating Vectors

A vector is a one-dimensional array of numbers. MATLAB allows creating two types of vectors −

• Row vectors
• Column vectors

Row vectors are created by enclosing the set of elements in square brackets, using space or comma to delimit the elements.

For example,

 Live Demo

r = [7 8 9 10 11]

MATLAB will execute the above statement and return the following result −

r =

   7    8    9   10   11 

Another example,

 Live Demo

r = [7 8 9 10 11];
t = [2, 3, 4, 5, 6];
res = r + t

MATLAB will execute the above statement and return the following result −

res =

         9         11         13         15         17

Column vectors are created by enclosing the set of elements in square brackets, using semicolon(;) to delimit the elements.

 Live Demo

c = [7;  8;  9;  10; 11]

MATLAB will execute the above statement and return the following result −

c =
       7       
       8       
       9       
      10       
      11  

Creating Matrices

A matrix is a two-dimensional array of numbers.

In MATLAB, a matrix is created by entering each row as a sequence of space or comma separated elements, and end of a row is demarcated by a semicolon. For example, let us create a 3-by-3 matrix as −

 Live Demo

m = [1 2 3; 4 5 6; 7 8 9]

MATLAB will execute the above statement and return the following result −

m =
       1              2              3       
       4              5              6       
       7              8              9   

[ Matlab Tutorial - Lession 1] - Syntax

MATLAB environment behaves like a super-complex calculator. You can enter commands at the >> command prompt.

MATLAB is an interpreted environment. In other words, you give a command and MATLAB executes it right away.

Hands on Practice

Type a valid expression, for example,

 Live Demo

5 + 5

And press ENTER

When you click the Execute button, or type Ctrl+E, MATLAB executes it immediately and the result returned is −

ans = 10

Let us take up few more examples −

 Live Demo

3 ^ 2        % 3 raised to the power of 2

When you click the Execute button, or type Ctrl+E, MATLAB executes it immediately and the result returned is −

ans = 9

Another example,

 Live Demo

sin(pi /2)   % sine of angle 90o

When you click the Execute button, or type Ctrl+E, MATLAB executes it immediately and the result returned is −

ans = 1

Another example,

 Live Demo

7/0        % Divide by zero

When you click the Execute button, or type Ctrl+E, MATLAB executes it immediately and the result returned is −

ans = Inf
warning: division by zero

Another example,

 Live Demo

732 * 20.3 

When you click the Execute button, or type Ctrl+E, MATLAB executes it immediately and the result returned is −

ans =  1.4860e+04

MATLAB provides some special expressions for some mathematical symbols, like pi for π, Inf for ∞, i (and j) for √-1 etc. Nan stands for 'not a number'.

Use of Semicolon (;) in MATLAB

Semicolon (;) indicates end of statement. However, if you want to suppress and hide the MATLAB output for an expression, add a semicolon after the expression.

For example,

 Live Demo

x = 3;
y = x + 5

When you click the Execute button, or type Ctrl+E, MATLAB executes it immediately and the result returned is −

y =  8

Adding Comments

The percent symbol (%) is used for indicating a comment line. For example,

x = 9      % assign the value 9 to x

You can also write a block of comments using the block comment operators % { and % }.

The MATLAB editor includes tools and context menu items to help you add, remove, or change the format of comments.

Commonly used Operators and Special Characters

MATLAB supports the following commonly used operators and special characters −

Operator	Purpose
+	Plus; addition operator.
-	Minus; subtraction operator.
*	Scalar and matrix multiplication operator.
.*	Array multiplication operator.
^	Scalar and matrix exponentiation operator.
.^	Array exponentiation operator.
\	Left-division operator.
/	Right-division operator.
.\	Array left-division operator.
./	Array right-division operator.
:	Colon; generates regularly spaced elements and represents an entire row or column.
( )	Parentheses; encloses function arguments and array indices; overrides precedence.
[ ]	Brackets; enclosures array elements.
.	Decimal point.
…	Ellipsis; line-continuation operator
,	Comma; separates statements and elements in a row
;	Semicolon; separates columns and suppresses display.
%	Percent sign; designates a comment and specifies formatting.
_	Quote sign and transpose operator.
._	Nonconjugated transpose operator.
=	Assignment operator.

Special Variables and Constants

MATLAB supports the following special variables and constants −

Name	Meaning
ans	Most recent answer.
eps	Accuracy of floating-point precision.
i,j	The imaginary unit √-1.
Inf	Infinity.
NaN	Undefined numerical result (not a number).
pi	The number π

Naming Variables

Variable names consist of a letter followed by any number of letters, digits or underscore.

MATLAB is case-sensitive.

Variable names can be of any length, however, MATLAB uses only first N characters, where N is given by the function namelengthmax.

Saving Your Work

The save command is used for saving all the variables in the workspace, as a file with .mat extension, in the current directory.

For example,

save myfile

You can reload the file anytime later using the load command.

load myfile