MATLAB MODULE 1
MATLAB Window Environment and the Base Program
Starting MATLAB
On the Windows desktop, the installer usually creates a shortcut icon for starting MATLAB; doubleclicking 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.
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:
>> 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.
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).
>> x=34*j+10/pi+5.678+7.890+2^21.89 >> x=34*j+10/pi+5.678... +7.890+2^21.89
+ addition, 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.
Variables j = 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
For example, two complex numbers 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
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 .
>> 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.
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.
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.
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 pulldown 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 MATLABspecific 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
mfiles 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. Doubleclicking 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 rightclick 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 doubleclicking 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 uparrow key. This helps in editing previous commands.
Selecting one or more commands and rightclicking 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.
