# Writing scripts to solve problems

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Upon running the file, the output.txt file will display the following:

The radius of acetylene bottle: 0.3 meters The height of cylindrical part of acetylene bottle: 1.5 metersThe volume of the acetylene bottle: 0.480664 cubic meters.

## Loops

In programming, a loop executes a set of code a specified number of times or until a condition is met.

## For loop

This loop iterates an index variable from an initial value using a specified increment to a final value and runs a set of code. The for loop syntax is the following: for loop_index=vector_statement code... codeend

Calculate $y=\cos x$ for $-\pi \le x\le \pi$ using an increment of $\frac{\pi }{4}$ . for x=-pi:pi/4:pi y=cos(x);fprintf('%8.3f %8.2f \n',x,y); end

In the brief script above, $x$ is the loop index that is initiated from $-\pi$ and incremented with $\frac{\pi }{4}$ to a final value of $\pi$ . At the end of each increment, $y=\cos x$ is calculated and displayed with the fprintf command. This process continues until $x=\pi$ .

From a previous exercise we know \n creates a new line when included in the fprintf command. Here, we also use %8.3f to specify eight spaces and three decimal places for the first variable x. Likewise %8.2f specifies the formatting for the second variable y but in this case, y is displayed with two decimal places. The result is the following: -3.142 -1.00 -2.356 -0.71-1.571 0.00 -0.785 0.710.000 1.00 0.785 0.711.571 0.00 2.356 -0.713.142 -1.00

We can improve our code by adding formatting lines as follows: clear; clc; fprintf(' x cos(x)\n') % title rowfprintf(' ----------------\n') % title row for x=-pi:pi/4:pi % loop_index=inital_value:increment_value:final_valuey=cos(x); % code to calculate cos(x) fprintf('%8.3f %8.2f \n',x,y); % code to print the output to screenend

Screen output: x cos(x) -----------------3.142 -1.00 -2.356 -0.71-1.571 0.00 -0.785 0.710.000 1.00 0.785 0.711.571 0.00 2.356 -0.713.142 -1.00

## While loop

Like the for loop, a while loop executes blocks of code over and over again however it runs as long as the test condition remains true. The syntax of a while loop is while test_condition code... codeend

Using a while loop, calculate $y=\cos x$ for $-\pi \le x\le \pi$ using an increment of $\frac{\pi }{4}$ .

This time we need to initialize the x value outside the loop and then state the test condition in the first line of the while loop. We also need to create an increment statement within the while loop: x=-pi; while x<=pi y=cos(x);fprintf('%8.3f %8.2f \n',x,y); x = x + (pi/4);end

The result is the same as that of the previous example: -3.142 -1.00 -2.356 -0.71-1.571 0.00 -0.785 0.710.000 1.00 0.785 0.711.571 0.00 2.356 -0.713.142 -1.00

Now we can improve the code by adding extra formatting lines and comments: clear; clc; fprintf(' x cos(x)\n') % title rowfprintf(' ----------------\n') % title row x=-pi; % initiating the x valuewhile x<=pi % stating the test condition y=cos(x); % calculating the value of yfprintf('%8.3f %8.2f \n',x,y); % printing a and y x = x + (pi/4); % iterating to the next stepend

The result should look the same as before. x cos(x) -----------------3.142 -1.00 -2.356 -0.71-1.571 0.00 -0.785 0.710.000 1.00 0.785 0.711.571 0.00 2.356 -0.713.142 -1.00

## The diary Function

Instead of writing a script from scratch, we sometimes solve problems in the Command Window as if we are using a scientific calculator. The steps we perform in this fashion can be used to create an m-file. For example, the diary function allows us to record a MATLAB session in a file and retrieve it for review. Reviewing the file and by copying relevant parts of it and pasting them in to an m-file, a script can be written easily.

Typing diary at the MATLAB prompt toggles the diary mode on and off. As soon as the diary mode is turned on, a file called diary is created in the current directory. If you like to save that file with a specific name, say for example problem16, type
>>diary problem16.txt .
A file named problem16.txt will be created. The following is the content of a diary file called problem16.txt. Notice that in that session, the user is executing the four files we created earlier. The user's keyboard input and the resulting display output is recorded in the file. The session is ended by typing diary which is printed in the last line. This might be useful to create a record of your work to hand in with a lab or to create the beginnings of an m-file.

AcetyleneBottle Vol_total =0.4807 AcetyleneBottleInteractiveEnter the radius of acetylene bottle in meters .3 Enter the height of cylinderical part of acetylene bottle in meters 1.5Vol_total = 0.4807AcetyleneBottleInteractiveDisp This script computes the volume of an acetylene bottleEnter the radius of acetylene bottle in meters .5 Enter the height of cylinderical part of acetylene bottle in meters 1.6The volume of the acetylene bottle is1.5184 AcetyleneBottleInteractiveDisp1This script computes the volume of an acetylene bottle:Enter the radius of acetylene bottle in meters .9 Enter the height of cylinderical part of acetylene bottle in meters 1.9The volume of the acetylene bottle is 6.3617 cubic meters.diary

## Style guidelines

Try to apply the following guidelines when writing your scripts:

• Share your code or programs with others, consider adopting one of Creative Commons or GNU General Public License schemes
• Include your name and contact info in the opening lines
• Use comments liberally
• Group your code and use proper indentation
• Use white space liberally
• Use descriptive names for your variables
• Use descriptive names for your m-files

## Summary of key points

1. A script is a file containing a sequence of MATLAB statements. Script files have a filename extension of .m.
2. Functions such as input , disp and num2str can be used to make scripts interactive,
3. fopen , fprintf and fclose functions are used to create output files,
4. A for loop is used to repeat a specific block of code a definite number of times.
5. A while loop is used to repeat a specific block of code an indefinite number of times, until a condition is met.
6. The diary function is useful to record a MATLAB command window session from which an m-file can be easily created,
7. Various style guidelines covered here help improve our code.

#### Questions & Answers

can someone help me with some logarithmic and exponential equations.
Jeffrey Reply
sure. what is your question?
ninjadapaul
20/(×-6^2)
Salomon
okay, so you have 6 raised to the power of 2. what is that part of your answer
ninjadapaul
I don't understand what the A with approx sign and the boxed x mean
ninjadapaul
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
ninjadapaul
oops. ignore that.
ninjadapaul
so you not have an equal sign anywhere in the original equation?
ninjadapaul
Commplementary angles
Idrissa Reply
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.
Kevin Reply
a perfect square v²+2v+_
Dearan Reply
kkk nice
Abdirahman Reply
algebra 2 Inequalities:If equation 2 = 0 it is an open set?
Kim Reply
or infinite solutions?
Kim
The answer is neither. The function, 2 = 0 cannot exist. Hence, the function is undefined.
Al
y=10×
Embra Reply
if |A| not equal to 0 and order of A is n prove that adj (adj A = |A|
Nancy Reply
rolling four fair dice and getting an even number an all four dice
ramon Reply
Kristine 2*2*2=8
Bridget Reply
Differences Between Laspeyres and Paasche Indices
Emedobi Reply
No. 7x -4y is simplified from 4x + (3y + 3x) -7y
Mary Reply
is it 3×y ?
Joan Reply
J, combine like terms 7x-4y
Bridget Reply
im not good at math so would this help me
Rachael Reply
yes
Asali
I'm not good at math so would you help me
Samantha
what is the problem that i will help you to self with?
Asali
how do you translate this in Algebraic Expressions
linda Reply
Need to simplify the expresin. 3/7 (x+y)-1/7 (x-1)=
Crystal Reply
. After 3 months on a diet, Lisa had lost 12% of her original weight. She lost 21 pounds. What was Lisa's original weight?
Chris Reply
what's the easiest and fastest way to the synthesize AgNP?
Damian Reply
China
Cied
types of nano material
abeetha Reply
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.
Ramkumar Reply
what is nano technology
Sravani Reply
what is system testing?
AMJAD
preparation of nanomaterial
Victor Reply
Yes, Nanotechnology has a very fast field of applications and their is always something new to do with it...
Himanshu Reply
good afternoon madam
AMJAD
what is system testing
AMJAD
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
Prasenjit Reply
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.
Ali Reply
the Beer law works very well for dilute solutions but fails for very high concentrations. why?
bamidele Reply
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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Source:  OpenStax, A brief introduction to engineering computation with matlab. OpenStax CNX. Nov 17, 2015 Download for free at http://legacy.cnx.org/content/col11371/1.11
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