Starting MATLAB
On
the Windows desktop, the installer usually creates a shortcut icon for
starting MATLAB; double-clicking on this icon opens MATLAB desktop.
The
MATLAB desktop is an integrated development environment for working
with MATLAB suite of toolboxes, directories, and programs. We see in
Fig. M1.1 that there are four panels, which represent:
- Command Window
- Current Directory
- Workspace
- Command History
A particular window can be activated by clicking anywhere inside its borders.
Fig. M1.1 MATLAB Desktop (version 7.0, release 14)
Desktop layout can be changed by following
Desktop
--> Desktop Layout
from the main menu as shown in Fig. M1.2 (Default option gives Fig. M1.1).
Fig. M1.2 Changing Desktop Layout to History and Command Window option
Command Window
We type all our commands in this window at the prompt ( >> ) and press return 
to see the results of our operations. Type the command ver
on the command prompt to get information about MATLAB version, license
number, operating system on which MATLAB is running, JAVA support
version, and all installed toolboxes. If MATLAB don't regard to your
speed of reading and flush the entire output at once, just type more on before supplying command to see one screen of output at a time. Clicking the What's New button
located on the desktop shortcuts toolbar, opens the release notes for
release 14 of MATLAB in Help window. These general release notes give
you a quick overview of what products have been updated for Release 14.
to see the results of our operations. Type the command ver
on the command prompt to get information about MATLAB version, license
number, operating system on which MATLAB is running, JAVA support
version, and all installed toolboxes. If MATLAB don't regard to your
speed of reading and flush the entire output at once, just type more on before supplying command to see one screen of output at a time. Clicking the What's New button
located on the desktop shortcuts toolbar, opens the release notes for
release 14 of MATLAB in Help window. These general release notes give
you a quick overview of what products have been updated for Release 14.
Working with Command Window
allows the user to use MATLAB as a versatile scientific calculator for
doing online quick computing. Input information to be processed by the
MATLAB commands can be entered in the form of numbers and arrays.
As an example of a simple interactive calculation, suppose that you want to calculate the torque ( T ) acting on 0.1 kg mass ( m ) at 
swing 
of the pendulum of length ( l ) 0.2 m. For small values of swing, T is given by the formula 
. This can be done in the MATLAB command window by typing:
swing of the pendulum of length ( l ) 0.2 m. For small values of swing, T is given by the formula . This can be done in the MATLAB command window by typing:
>> torque = 0.1*9.8*0.2*pi/6 
MATLAB responds to this command by:
torque =
0.1026
MATLAB calculates and stores the answer in a variable torque (in fact, a 
array) as soon as the Enter key is pressed. The variable torque can be used in further calculations. 
is predefined in MATLAB; so we can just use pi without declaring it to be 3.14….Command window indicating these operations is shown in Fig. M1.3.
array) as soon as the Enter key is pressed. The variable torque can be used in further calculations. is predefined in MATLAB; so we can just use pi without declaring it to be 3.14….Command window indicating these operations is shown in Fig. M1.3. 
Fig. M1.3 Command Window for quick scientific calculations ( text in colored boxes corresponds to explanatory notes ).
If any statement is followed by a semicolon,
>> m = 0.1; 
>> l = 0.2; 
>> g = 9.8; 
the
display of the result is suppressed. The assignment of the variable has
been carried out even though the display is suppressed by the
semicolon. To view the assignment of a variable, simply type the
variable name and hit Enter. For example:
>> torque=m*g*l*pi/6; 
>> torque 
torque =
0.1026
It
is often the case that your MATLAB sessions will include intermediate
calculations whose display is of little interest. Output display
management has the added benefit of increasing the execution speed of
the calculations, since displaying screen output takes time.
Variable
names begin with a letter and are followed by any number of letters or
numbers (including underscore). Keep the name length to 31 characters,
since MATLAB remembers only the first 31 characters. Generally we do not
use extremely long variable names even though they may be legal MATLAB
names. Since MATLAB is case sensitive, the variables
A and
a are different.
When a statement being entered is too long for one line, use three periods, … , followed by 
to indicate that the statement continues on the next line. For example,
the following statements are identical (see Fig. M1.4).
to indicate that the statement continues on the next line. For example,
the following statements are identical (see Fig. M1.4).
>> x=3-4*j+10/pi+5.678+7.890+2^2-1.89
>> x=3-4*j+10/pi+5.678...
+7.890+2^2-1.89
+ addition, 
subtraction, * multiplication, / division, and ^ power are usual arithmetic operators.
subtraction, * multiplication, / division, and ^ power are usual arithmetic operators.
The basic MATLAB trigonometric commands are sin, cos, tan, cot, sec and csc. The inverses 
, etc., are calculated by asin, acos, etc. The same is true for hyperbolic functions. Some of the trigonometric operations are shown in Fig M1.5.
, etc., are calculated by asin, acos, etc. The same is true for hyperbolic functions. Some of the trigonometric operations are shown in Fig M1.5.
Variables j = 
and i = 
are predefined in MATLAB and are used to represent complex numbers.
and i = are predefined in MATLAB and are used to represent complex numbers. 
Fig. M1.4 Command Window with example operations
Fig. M1.5 Example trigonometric calculations
MATLAB representation of complex number 
:
: 
or 
The later case is always interpreted as a complex number, whereas, the former case is a complex number in MATLAB only if j has not been assigned any prior local value.
MATLAB representation of complex number 
:
: 
or 
or 
In Cartesian form, arithmetic additions on complex numbers are as simple as with real numbers. Consider two complex numbers 
and 
. Their sum 
is given by
and . Their sum is given by 
For example, two complex numbers 
and 
can be added in MATLAB as:
and can be added in MATLAB as:
>> z1=3+4j; 
>> z2=1.8+2j; 
>> z=z1+z2 
z =
4.8000 + 6.0000i
Multiplication of two or
more complex numbers is easier in polar/complex exponential form. Two
complex numbers with radial lengths 
and 
are given with angles 
and 
rad. We change 
to radians to give 
rad= 
rad. The complex exponential form of their product 
is given by
and are given with angles and rad. We change to radians to give rad= rad. The complex exponential form of their product is given by 
This can be done in MATLAB by:
>> theta1=(35/180)*pi; 
>> z1=2*exp(theta1*j); 
>> z2=2.5*exp(0.25*pi*j); 
>> z=z1*z2 
z =
0.8682 - 4.9240j
Magnitude and phase of a complex number can be calculated in MATLAB by commands abs and angle. The following MATLAB session shows the magnitude and phase calculation of complex numbers 
and 
.
and .
>> abs(5*exp(0.19*pi*j)) 
ans =
5
>> angle(5*exp(0.19*pi*j)) 
ans =
0.5969
>> abs(1/(2+sqrt(3)*j)) 
ans =
0.3780
>> angle(1/(2+sqrt(3)*j)) 
ans =
-0.7137
Some complex numbered calculations are shown in Fig. M1.6.
Fig. M1.6 Example complex numbered calculations
The mathematical quantities 
and 
are calculated with exp(x), log10(x), and log(x), respectively.
and are calculated with exp(x), log10(x), and log(x), respectively.
All computations in MATLAB are performed in double precision .
The screen output can be displayed in several formats. The default
output format contains four digits past the decimal point for
nonintegers. This can be changed by using the format command. Remember that the format command affects only how numbers are displayed, not how MATLAB computes or saves them. See how MATLAB prints 
in different formats.
in different formats. |
Format command at MATLAB prompt
|
Display format
|
| format short |
31.4159
|
|
format short e
|
3.1416e+001
|
|
format long
|
31.41592653589793
|
|
format long e
|
3.141592653589793e+001
|
|
format short g
|
31.416
|
|
format long g
|
31.4159265358979
|
|
format bank
|
31.42
|
The
following exercise will enable the readers to quickly write various
mathematical formulas, interpreting error messages, and syntax related
issues.
|
, check that 
. 
that 
. 
that 
. 
. 
in MATLAB as 
and then enter 
using MATLAB.
.
for 
for 
. 
for 
. 
.
Current Directory Window
This
window (Fig. M1.7) shows the directory, and files within the directory
which are in use currently in MATLAB session to run or save our program
or data. The default directory is ‘C:\MATLAB7\work'. We can change this
directory to the desired one by clicking on the square browser button
near the pull-down window.
Fig. M1.7 Current directory window
One
can also use command line options to deal with directory and file
related issues. Some useful commands are shown in Table M1.1.
Table M1.1
|
Command
|
Usage
|
|
cd, pwd
|
To see the current directory
|
|
cd ..
|
To go one directory back from the current directory
|
|
cd \
|
To go back to the root directory
|
|
cd dir_name
|
To change to the directory named dir_name
|
|
ls or dir
|
To see the list of files and subdirectories within the current directory
|
|
what
|
Lists MATLAB-specific files in the directory. MATLAB specific files are with the extensions .m, .mat, .mdl, .mex, and
.p.
|
mkdir (parentdir,dir_name)
mkdir dir_name
|
Makes new directory with the name dir_name in the parent directory specified by parentdir .
When supplied with only dir_name, it creates new directory within the current directory
|
delete file_name
delete *.m
|
Deletes file from the current directory.
Deletes all
m-files from the current directory.
|
MATLAB desktop snapshot showing selected commands from Table M1.1 are shown in Fig. M1.8.
Workspace
Workspace window
shows the name, size, bytes occupied, and class of any variable defined
in the MATLAB environment. For example in Fig.M1.9, ‘b' is 1 X 4 size
array of data type double
and thus occupies 32 bytes of memory. Double-clicking on the name of
the variable opens the array editor (Fig. M1.10). We can change the
format of the data (e.g., from integer to floating point), size of the
array (for example, for variable A, from 3 X 4 array to 4 X 4 array) and can also modify the contents of the array.
Fig. M1.8 Example directory related commands
If
we right-click on the name of a variable, a menu pops up, which shows
various operations for the selected variable, such as: open the array
editor, save selected variable for future usage, copy, duplicate, and
delete the variable, rename the variable, editing the variable, and
various plotting options for the selected variable.
Fig. M1.9 Entries in the Workspace
Fig. M1.10 Array editor window
Workspace related commands are listed in Table M1.2.
Table M1.2
| Command | Usage |
| who |
Lists variables currently in the workspace
|
| whos |
Lists more information about each variable including size, bytes stored in the computer, and class type of the variables
|
| clear |
Clears the workspace. All variables are removed
|
| clear all |
Removes all variables and functions from the workspace. This can also be done by selecting
Edit
from the main menu bar and then clicking the option
Clear Workspace
.
|
| clear var1 var2 |
Removes only var1 and var2 from the workspace.
|
For example, see the following MATLAB session for the use of
who and
whos
commands.
>> who
Your variables are:
A b
>> whos
| Name | Size | Bytes | Class |
| A | 3x4 | 96 | double array |
| b | 1x4 | 32 |
double array |
Grand total is 16 elements using 128 bytes
Command History Window
This
window (Fig. M1.11) contains a record of all the commands that we type
in the command window. By double-clicking on any command, we can execute
it again. It stores commands from one MATLAB session to another,
hierarchically arranged in date and time. Commands remain in the list
until they are deleted.
Fig. M1.11 Command history window
Commands can also be recalled with the up-arrow 
key. This helps in editing previous commands.
key. This helps in editing previous commands.
Selecting
one or more commands and right-clicking them, pops up a menu, allowing
users to perform various operations such as copy, evaluate, or delete,
on the selected set of commands. For example, two commands are being
deleted in Fig. M1.12.
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