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Script files, also called M- files as they
have extension
.m
, make MATLAB programming much more efficient than
entering individual commands at the command prompt. A script fileconsists of MATLAB commands that together perform a specific task.
The M-file is a text file which can be created and edited by anyplain text editor like Notepad, emacs or the built-in MATLAB
editor. To create a script in MATLAB use:
File - New - M -File
from the menu. An example script
is shown below.
Our first script.
n = 0:pi/100:2*pi; %create an index vector
y = cos(2*pi*n); %create a vector yplot(n,y); %plot y versus n
As shown above the
%
-sign allows for comments. Saving the script as
foo.m
it can be executed as
foo
from the command prompt or by clicking the run
button in the MATLAB editor. Script files are very practical and should be the preferred alternative compared to the command promptin most cases.
As in most programming languages program flow can be controlled by using statements such as
for
,
while
,
if
,
else
,
elseif
, and
switch
.
These statements can be used both in M-files and at the command prompt, the latter being highlyinconvenient. Below we show some examples. Use help to get more details.
for
- To print "Hello World" 10 times write
for n=1:10
disp('Hello World')end
for
loops can in many cases be avoided by
vectorizing your code, more about that
later .if
,
else
and
elseif
- Classics that never go out of style.
if a == b
a = b + 1elseif a>b
a = b - 1else
a = bend
Sometimes it is convenient to create your own functions for use in MATLAB. Functions are program routines,usually implemented in M-files. Functions can take input arguments and return output arguments. They operate on variables within theirown workspace, separate from the workspace you access at the MATLAB command prompt.
Create a function for calculating the sum of the $N+1$ first terms of geometric series. Assume $N$∞ .
Solution: The sum of the N + 1 terms of a geometric
series is given by
$\mathrm{ssum}=\sum_{n=0}^{N} a^{n}$ .
An implementation of this sum as a function accepting the input arguments
$a$ and
$N$ is shown below.
function ssum = geom(a,N)
n=0:N;ssum = sum(a.^n);
end
The function
geom
can then be called, e.g from the command prompt.
The function call
geom(0.9,10)
returns 6.8619.
To illustrate some more MATLAB programming we take on the task of creating a MATLAB function that will compute the sum of an arbitrary geometric series, $\mathrm{ssum}=\sum_{n=0}^{N} a^{n}$ .
Create a function to calculate the sum of an arbitrary geometric series.
Solution: For
$N$∞ we know that the sum converges regardless of
$a$ .
As
$N$ goes to
$$∞ the sum converges only for
$a< 1$ , and the sum is given by the formula
$\sum_{n=0} $∞
function ssum = geomInf(a,N)
if(N==inf)if(abs(a)>=1)
error('This geometric series will diverge.');else
ssum=1/(1-a);end
elsen=0:N;
ssum = sum(a.^n);end
end
Note that in the two examples above we could have used the formula for the sum of a finite geometric series. However we chose to create a vector and use the function
sum
to illustrate MATLAB concepts.
Wouldn't it be great to learn from the best? Using the command
type
followed by a function name the source code of the function is displayed.
As the built in functions are written by people with excellent knowledge ofMATLAB, this is a great feature for anyone interested in learning more
about MATLAB.
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