0.3 Scripts and functions in matlab

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This module introduces the script and function environment in MATLAB.

Script files

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.

Program flow

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

User defined functions

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 $\sum_{n=0}$ a n 1 1 a . A possible implementation is given as: 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.

Learn from existing code

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.

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
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
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
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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