# 9.9 An introduction to matlab: editing files and creating functions

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This module is part of the collection, A First Course in Electrical and Computer Engineering . The LaTeX source files for this collection were created using an optical character recognition technology, and because of this process there may be more errors than usual. Please contact us if you discover any errors.

If you quit MATLAB now, all the commands you have typed will be lost. This is where the Edit window is useful. If you choose new from the File menu, a new window appears with the title Edit 1 : Untitled . In this window, you should type in all the commands you would like MATLAB to execute atonce. When you are finished typing, you may save the file by choosing save or save as in the file menu and by entering a name for the file. If the edit window is active (that is, if it appears in front), then choose save and go from the file menu to save the file and execute it. If the command window is active,then you can execute the file by entering its name.

Editing Files. To test your understanding of file editing, enter the following commands in a file named myfile:

You do not have to type the % sign and the text that follows it. These are simply comments in a file. They are ignored by the MATLAB interpreter.You should, however, make a habit of adding comments (preceded by %) to your file if you want to be able to understand programs that have been writtenlong ago.

Do not forget to save your file. Such a file is called a script file . It contains MATLAB commands that could have been entered one by one in thecommand window. You have three ways to execute a script file:

1. with the edit window active, choose save and go from the file menu;
2. with the command window active, enter the file name; or
3. with the command window active, choose run script ... from the M-file menu. In this case, a menu pops up to ask you which file you want to execute.

Try each of these three methods in order to get used to their differences. Figure 1 shows the plot that you should get.

Creating Functions. MATLAB puts many commands at your disposal, and you just have to enter their names (with or without arguments) to execute them. Some commands are built in to MATLAB, and others arecontained in files to which you have access (not to modify them, but to see how things are done). You can try to display the contents of a command filein the command window by entering the command type filename. Enter type plot. You should get the message

This means that the commandis a build-in function and thus cannot be typed by the user (it is compiled with the program). Similarly, try to typethe function file containing the commandby entering the command. You should get type sinh

This is a typical example of a function file . It differs from a script file by the fact that the first line contains the word. What it does is make the commandequivalent to the command. The variableis the input argument (there could be more than one), and y is the output argument (there also could be more than one). The second line contains comments about the function and its arguments. They can spreadto several lines. Display them by typing the command. The third line contains the actual function commands (there could also be several lines). help sinh

As an exercise, enter the function: perp(x)

Evaluateon various complex numbers. Replace the last line by;. Do you get the same result? Why? y = x*j

Note that local variables are just that– local . Only the input and out- put arguments are kept in memory after the function is called and executed.For more on functions and multiple arguments, see the MATLAB manual. In the previous example, the variable $j$ is local. If, before using the function, you use the same variable $j$ , its contents will not be affected by the command. Verify this. perp(z)

Normally, while a file (script or function) is executed, the commands are not displayed on the command window. Just the results are displayed.The commandallows you to view all the instructions. This is useful for debugging and demonstrations. It is turned off by typing. echo off

how do they get the third part x = (32)5/4
can someone help me with some logarithmic and exponential equations.
20/(×-6^2)
Salomon
okay, so you have 6 raised to the power of 2. what is that part of your answer
I don't understand what the A with approx sign and the boxed x mean
it think it's written 20/(X-6)^2 so it's 20 divided by X-6 squared
Salomon
I'm not sure why it wrote it the other way
Salomon
I got X =-6
Salomon
ok. so take the square root of both sides, now you have plus or minus the square root of 20= x-6
oops. ignore that.
so you not have an equal sign anywhere in the original equation?
Commplementary angles
hello
Sherica
im all ears I need to learn
Sherica
right! what he said ⤴⤴⤴
Tamia
hii
Uday
what is a good calculator for all algebra; would a Casio fx 260 work with all algebra equations? please name the cheapest, thanks.
a perfect square v²+2v+_
kkk nice
algebra 2 Inequalities:If equation 2 = 0 it is an open set?
or infinite solutions?
Kim
The answer is neither. The function, 2 = 0 cannot exist. Hence, the function is undefined.
Al
y=10×
if |A| not equal to 0 and order of A is n prove that adj (adj A = |A|
rolling four fair dice and getting an even number an all four dice
Kristine 2*2*2=8
Differences Between Laspeyres and Paasche Indices
No. 7x -4y is simplified from 4x + (3y + 3x) -7y
is it 3×y ?
J, combine like terms 7x-4y
how do you translate this in Algebraic Expressions
Need to simplify the expresin. 3/7 (x+y)-1/7 (x-1)=
. After 3 months on a diet, Lisa had lost 12% of her original weight. She lost 21 pounds. What was Lisa's original weight?
what's the easiest and fastest way to the synthesize AgNP?
China
Cied
types of nano material
I start with an easy one. carbon nanotubes woven into a long filament like a string
Porter
many many of nanotubes
Porter
what is the k.e before it land
Yasmin
what is the function of carbon nanotubes?
Cesar
I'm interested in nanotube
Uday
what is nanomaterials​ and their applications of sensors.
what is nano technology
what is system testing?
preparation of nanomaterial
Yes, Nanotechnology has a very fast field of applications and their is always something new to do with it...
what is system testing
what is the application of nanotechnology?
Stotaw
In this morden time nanotechnology used in many field . 1-Electronics-manufacturad IC ,RAM,MRAM,solar panel etc 2-Helth and Medical-Nanomedicine,Drug Dilivery for cancer treatment etc 3- Atomobile -MEMS, Coating on car etc. and may other field for details you can check at Google
Azam
anybody can imagine what will be happen after 100 years from now in nano tech world
Prasenjit
after 100 year this will be not nanotechnology maybe this technology name will be change . maybe aftet 100 year . we work on electron lable practically about its properties and behaviour by the different instruments
Azam
name doesn't matter , whatever it will be change... I'm taking about effect on circumstances of the microscopic world
Prasenjit
how hard could it be to apply nanotechnology against viral infections such HIV or Ebola?
Damian
silver nanoparticles could handle the job?
Damian
not now but maybe in future only AgNP maybe any other nanomaterials
Azam
Hello
Uday
I'm interested in Nanotube
Uday
this technology will not going on for the long time , so I'm thinking about femtotechnology 10^-15
Prasenjit
can nanotechnology change the direction of the face of the world
At high concentrations (>0.01 M), the relation between absorptivity coefficient and absorbance is no longer linear. This is due to the electrostatic interactions between the quantum dots in close proximity. If the concentration of the solution is high, another effect that is seen is the scattering of light from the large number of quantum dots. This assumption only works at low concentrations of the analyte. Presence of stray light.
the Beer law works very well for dilute solutions but fails for very high concentrations. why?
how did you get the value of 2000N.What calculations are needed to arrive at it
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