matlab homework

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MATLAB Introduction II

Programming and Scripts

Programming and Scripts

• The simplest type of MATLAB program is

called a script.

• A script is a file with a .m extension that

contains multiple sequential lines of MATLAB

commands and function calls.

• You can run a script by typing its name at the

command line.

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Sample Script

• To create a script, use the edit command,

• This opens a blank file named plotrand.m

• Enter some code that plots a vector of random data:

edit plotrand

n = 50;

r = rand(n,1);

plot(r)

Sample Script • Next, add code that draws a horizontal line on

the plot at the mean:

m = mean(r);

hold on

plot([0,n],[m,m])

hold off

title('Mean of Random Uniform Data')

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Sample Script • Whenever you write code, it is a good practice to add

comments that describe the code. Comments allow others to

understand your code, and can refresh your memory when you

return to it later. Add comments using the percent (%) symbol.

% Generate random data from a uniform distribution

% and calculate the mean. Plot the data and the mean.

n = 50; % 50 data points

r = rand(n,1);

plot(r)

% Draw a line from (0,m) to (n,m)

m = mean(r);

hold on

plot([0,n],[m,m])

hold off

title('Mean of Random Uniform Data')

Sample Script

• Save the file in the current folder. To run the

script, type its name at the command line:

• You can also run scripts from the Editor by

pressing the Run button, .

plotrand

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Sample Script

• You will have something like this.

0 5 10 15 20 25 30 35 40 45 50 0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

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Mean of Random Uniform Data

Loops and Conditional Statements

• Within a script, you can loop over sections of code

and conditionally execute sections using the

keywords for, while, if, and switch.

• For example, create a script named calcmean.m that

uses a for loop to calculate the mean of five random

samples and the overall mean.

edit calcmean.m

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Loops and Conditional Statements

• Now, modify the for loop so that you can view the results at each iteration. Display text in the Command Window that includes the current iteration number, and remove the semicolon from the assignment to sampleMean.

nsamples = 5;

npoints = 50;

for k = 1:nsamples

currentData = rand(npoints,1);

sampleMean(k) = mean(currentData);

end

overallMean = mean(sampleMean)

Loops and Conditional Statements

• When you run the script, it displays the

intermediate results, and then calculates the

overall mean.

for k = 1:nsamples

iterationString = ['Iteration #',int2str(k)];

disp(iterationString)

currentData = rand(npoints,1);

sampleMean(k) = mean(currentData)

end

overallMean = mean(sampleMean)

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Loops and Conditional Statements • You will have something like this in the command

window. Iteration #1

sampleMean =

0.4899

Iteration #2

sampleMean =

0.4899 0.4505

Iteration #3

sampleMean =

0.4899 0.4505 0.4844

Iteration #4

sampleMean =

0.4899 0.4505 0.4844 0.4642

Iteration #5

sampleMean =

0.4899 0.4505 0.4844 0.4642 0.5447

overallMean =

0.4867

Loops and Conditional Statements

• In the Editor, add conditional statements to

the end of calcmean.m that display a different

message depending on the value of

overallMean.

if overallMean < .49

disp('Mean is less than expected')

elseif overallMean > .51

disp('Mean is greater than expected')

else

disp('Mean is within the expected range')

end

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Loops and Conditional Statements

• Run calcmean and verify that the correct

message displays for the calculated

overallMean. For example:

overallMean =

0.5178

Mean is greater than expected

Script Locations • MATLAB looks for scripts and other files in certain

places. To run a script, the file must be in the current folder or in a folder on the search path.

• By default, the MATLAB folder that the MATLAB Installer creates is on the search path. If you want to store and run programs in another folder, add it to the search path. Select the folder in the Current Folder browser, right-click, and then select Add to Path.

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Homework 1. Write a script named Homeworka2.m with the following

information using a for loop with x ranging from x = -5 to 5

� = �� + 3�� − 10� − 24

Plot (x,y) and label x-, y-axes and title of the graph. Print your

script and your plot.

2. Write a script named using j = rand(50, 1) from last to

generate 50 random numbers. In your script find max(j), min(j),

median(j) std(j) mean(j). End your script with this

Print the script and command window displayed answer

if median(j) > mean(j)

disp('Mean is less than Median!')

elseif median(j) < mean(j)

disp('Mean is greater than Median! ')

elseif abs(median(j)- mean(j))<0

disp('there is no difference!')

end