# INTRODUCTION TO MATLAB

**3.1 Manipulating Matrices**

The symbols for basic arithmetic operations with matrices are:

+ for addition —e.g.,

- for subtraction —e.g.,

* for multiplication —e.g.,

for inverting a matrix:

/ or \ for division—e.g., or G\C for “right”
division or “left” division

Note that matrices must be conformable for these operations to be defined. Also
note that C/G

and that ,
which are generally** not** the same.

Other useful operators include:

’ for transposition—e.g.,

for the determinant—e.g.,

for the trace—e.g.,

for the eigenvalues—e.g., **
3.1.1 Concatenation:**

MATLAB can easily join matrices together to make a larger matrix:

**3.1.2 Element-by-Element Operations
**

Sometimes it’s useful to have MATLAB perform an operation on each element of a matrix. For

example,

MATLAB can also perform element-by-element multiplication—e.g., – and division—

e.g., ( or equivalently , ).

**3.2 Solving Linear Equations **

X = A\B: Denotes the solution to the matrix equation AX = B.

X = B/A: Denotes the solution to the matrix equation XA = B.

**4. Writing Simple Programs**

The capabilities of Matlab can be extended through programs written in its own
programming

language. It provides the standard constructs, such as loops and conditionals;
these constructs

can be used interactively to reduce the tedium of repetitive tasks, or collected
in programs stored

in (nothing more than a text file with
extension ).

**4.1 Script M-files**

If you just want to enter in some simple problems for MATLAB to solve , using the
Command

window is fast and easy. But you will often have a long sequence of commands on
many

variables for MATLAB to evaluate—sometimes for hundreds of repetitions! MATLAB
allows

you to type your commands in a text file, called a **script or M-File**, and
then have the commands

in the M-file evaluated just as if they were entered in the Command window.

To create an M-File, click on the New M-file icon on the MATLAB desktop toolbar,
or choose

**New/M-File** from the **File **menu. You can use the text window that
appears to enter commands.

Try entering

Now click the Run icon on the toolbar to execute your commands. MATLAB asks you
to save

your file before it is run; use the **Save file as**: dialog box to name and
save your file. In the

CSSCR lab, save your M-File to the /temp folder. (MATLAB may open a dialog box
asking

about your Current Directory, if so, select the option that changes your Current
Directory to the

/temp folder where you’ve saved your M-File.)

The results of running your M-File appear in the MATLAB command window.

**4.2 For Loops**

A For Loop executes a set of commands a given number of times . Try running this
simple

program from an M-File:

**4.3 While Loops**

A While Loop executes a set of commands repeatedly, until a controlling
expression is no longer

true.

**4.4 If-Else-End Conditional**

The If-Else-End construct evaluates a logical expression and executes a command,
or group of

commands , based on the value of that expression. Try running this simple program
from an M-File:

These constructs can be used together, or nested within themselves and/or one
another, allowing

you to write powerful programs in which the results of past calculations affect
subsequent

operations.

**4.5 The Current Directory and Search Path**

To use an M-File that you have created, MATLAB needs to know where to find it.
MATLAB

looks on a Search Path so you need to make sure that the directory in which you
saved your MFile

is on this path. The easiest way to do this is to make the directory in which
you’ve saved

your M-File the Current Directory.

Alternatively, you can put that directory on the Search Path by selecting **Set
Path in** File menu

or by typing the following in the Command window:

For example in the Econ grad computer lab you would type

when logged on with your userid.

**4.6 Function M-Files**

These M-Files differ from the script M-Files you’ve been working with in that
they accept input

arguments and return output arguments. A Function M-File operates on variables
contained

within its own workspace, which is separate from the workspace you’ve been
accessing from the

command line or through script M-Files. To write a function M-File, open a new
M-File and

type the following:

Now save your function M-File—you must save your file with
**exactly** the same name you gave

the function—test1.m in this example (make sure you save it to either the
current directory or a

directory that is on the search path). In the command window, enter any
conformable “a” and

“B” (note: you do not need to name them “a” and “B”—the function will operate on
any

conformable inputs that you give it). In the command window type the following:

Now call your function by typing

**5. Plotting Graphs **

MATLAB has powerful graphing features . To get started plotting graphs, try this
example of a

simple 2-D graph.

When the graph appears, use the menu and toolbar to modify it and/or copy and
paste it into a

Word document.

**6. Working With Data**

You will certainly need to export your results from MATLAB or import data from
other sources.

Let’s start by saving some of what we did until now. The basic command format is
the save

command followed by the name of the file to create. This is followed by a list
of the variables

which are to be saved in the file. To create an ASCII file which can be read by
a spreadsheet the

list of variables is followed by the command –ascii.

This saves the A, B, and C variables in a
MATLAB data

file (with .mat extension) in the current directory.

This saves all variables in the Workspace

in a ASCII file in the directory C.

Now let’s clear all variables in the workspace:

Loading data from a .mat file is easy. Just use
instead of the command .

Note that you can choose which variables to load. This command loads only A and
B, if you

wanted to load all variables you could simply write “load exampleFile”.

A quick method of importing text or binary data from a file (e.g., Excel files)
is to use the

MATLAB Import Wizard. Open the Import Wizard by selecting **File -> Import Data**
at the

Command Window.

Specify or browse for the file containing the data you want to import and you
will see a preview

of what the file contains. Select the data you want and click **Finish**.
(For more information, see

Help file for ‘Importing Text Data’)

Prev | Next |