lab05, CISC106, Fall 2006

Overview

This week's lab focuses on if/else from Chapter 3 of the textbook, and for loops from Chapter 4 of the textbook.

Prerequisites

Before starting this lab:

• You should already be comfortable with skills learned in labs 1 through 4.
• You should have already read Chapter 3 in the textbook
  • At the very least, you should have read the material on logical expressions and the if/else statement, on pages 91-113.
• You should have already read Chapter 4 in the textbook.
  • At the very least, you should have read the material that introduces the for loop on pp. 153-163.
• You may also want to review the fprintf function on pages 41-43, in Chapter 2.

Step-by-Step Instructions

Step 1: Preparing your lab05 directory, and copying files you will need

Step 1a: Create a new subdirectory for lab05

Create a new subdirectory ~/cisc106/lab05, and make that your working directory.

If you are not sure how to do this, then review the instructions from lab03, steps 1a through 1d.

Step 1b: Copy the files needed for this week's lab

There are two ways to copy the files for this week's lab. Read over both methods before deciding which one to use.

1. Download them from the web page http://www.udel.edu/CIS/106/pconrad/06F/labs/lab05
• If you are working on a PC or Mac with the student version of MATLAB, you'll need to use that method.
• To do this, go to the web site, and right click on each file, and do a "save as" into the lab05 directory on your hard drive
2. If you are working on strauss, copy them directly from the directory /www/htdocs/CIS/106/pconrad/06F/labs/lab05
   • This is the easier way, since you can get all the files at once. It is described below.

Copying all the files at once (if you are on strauss)

Assuming that you are already in ~/cisc106/lab05 as your current working directory, the following command will copy all the files you need.

• Pay attention to where the spaces go—right after the cp, and right after the *
• Don't forget the period (dot) at the end, which stands for the destination (the current directory)

>> !cp /www/htdocs/CIS/106/pconrad/06F/labs/lab05/* .
>> 

There are additional notes about this command at lab04, step 1b if you need to review how this command works.

Step 2: Learning about the if/else command, while loop, and for loop

First: there is nothing to turn in for Step 2

The work you do in step 2 of this lab is only for practice and learning. There is nothing to turn in from this step of the lab.

But don't skip this step.

You'll look pretty foolish if you end up asking questions about stuff you should have learned by doing this step.

It would also be a shame to miss some easy questions on the exam about stuff you could have learned by doing this step.

So, don't skip it.

Step 2a: Working with the if/else

The if/else is used to make a decision in MATLAB. It allows you to send MATLAB to choose between executing one set of command (the if part), and another set (the else part).

• A more complex version, the if/elseif/else allows one of several different choices. You can have as many elseifs as you need, but only one else at the very end.
• Although we won't see any examples in this week's lab, it is also possible to have an if with no else at all.

In your lab05 directory, you should find (at least) three files that you copied back in step 1b (there may be others too):

• ifElseExample.m
• ifElseExample2.m
• letterGrade.m

Use the type command or the edit command to look at the contents of these three files.

• If using SSH to access strauss from home, use emacs at the Unix prompt, instead of edit at the MATLAB prompt.

Also, run them and experiment with them, typing in different values until you are comfortable with how an if/else works.

If you are not sure what to do, check out these reminders:

• To type the contents of an M-file, use type filename.m
  • For example, to list the contents of ifElseExample2.m, enter type ifElseExample2.m at the MATLAB >> prompt.
• To bring up an M-file in the editor window, use edit filename.m
  • The edit command only works in the graphics interface to MATLAB
• To run an M-file, type its name without the .m
  • For example, to run letterGrade.m, you just type letterGrade at the MATLAB >> prompt.

Now, try this challenge for practice

This is not to "turn in"—it is only for practice.

1. Copy the file letterGrade.m to letterGrade2.m. Use the Unix cp command to do it, like this:

   >> !cp letterGrade.m letterGrade2.m
   >>
   

   • This command indicates that letterGrade.m, the first filename, is the source file (i.e where you are copying from).
   • You are copying the source file to a new file called letterGrade2.m (the second filename) which is the destination file (i.e. where you are copying to).
   • Remember that since the cp command is a Unix command, you have to put an exclamation mark (!)in front of it when you type it at the MATLAB >> prompt.
   • On the PC/Mac student version of MATLAB, you cannot use Unix commands, so use copyfile instead of !cp, or just copy the file through the regular Windows or Mac desktop
     
2. Edit the file letterGrade2.m so that in addition to producing grades such as A, B, C, D and F, it can also produce grades such as A-, B+, etc. Consult the following table (copied from the course syllabus) for guidelines.
   • Note that (73 <= grade < 77) is perfectly reasonable in a MATH class, but is it NOT acceptable in MATLAB!
   • To solve the problem correctly, you need to keep the if/elseif/elseif/else structure pretty much the same as it already is, and just add in more criteria
3. Once you've coded the solution, test it out to make sure it works.

Step 3: Write an M-file that outputs a table of Katrina information

Using the file listGrades.m as a model, your job is to write an M-file called lab05.m that

• reads the information from katrina.dat (which should be in your lab05 directory, copied in with all the other files),
• slices out column vectors for hour, day, and wind
• produces the following output:

At 18 hours GMT on 08/23/2005, Katrina was a Tropical Depression
At  0 hours GMT on 08/24/2005, Katrina was a Tropical Depression
At  6 hours GMT on 08/24/2005, Katrina was a Tropical Depression
At 12 hours GMT on 08/24/2005, Katrina was a Tropical Storm
At 18 hours GMT on 08/24/2005, Katrina was a Tropical Storm
At  0 hours GMT on 08/25/2005, Katrina was a Tropical Storm
At  6 hours GMT on 08/25/2005, Katrina was a Tropical Storm
At 12 hours GMT on 08/25/2005, Katrina was a Tropical Storm
At 18 hours GMT on 08/25/2005, Katrina was a Tropical Storm
At  0 hours GMT on 08/26/2005, Katrina was a Cat 1 Hurricane
At  6 hours GMT on 08/26/2005, Katrina was a Cat 1 Hurricane
At 12 hours GMT on 08/26/2005, Katrina was a Cat 1 Hurricane
At 18 hours GMT on 08/26/2005, Katrina was a Cat 2 Hurricane
etc...

Use the table at Wikipedia article about the Saffir-Simpson_Hurricane_Scale to come up with your scale for the various categories of storm.

You can use the Weather Underground's Hurricane Katrina Archive to check your results.

• Note that the last two entries in the Weather Underground's page indicate that Katrina had morphed from a "Tropical Depression" into an "Extratropical Storm". We won't worry about making that particular distinction—feel free to continue to use "Tropical Depression" for those last two lines of output.

Some hints:

• Since the hour, day and wind vectors are all the same length, it doesn't matter which one you use to control the ending value for the for loop index. That is, for k = 1:length(wind) and for k=1:length(day) both will result in exactly the same set of values for k.

Step 4: Create a diary file lab05.txt to show your work.

Create a diary file called lab05.txt in which you type out your lab05.m file, and then test it to show that it works.

• If you need a refresher, review the instructions at step 6 of lab01, and step 1e of lab02

This time, one run is sufficient to test your program since all of the program input comes from the katrina.dat data file.

Step 5: Submit two files on WebCT.

The two files you need to submit are lab05.m and lab05.txt. Upload these to WebCT and submit.

That's it for lab05!

Grading

1. lab05.m (60 pts)
2. lab05.txt (30 pts)
3. Generally submitting everything according to instructions: 10 pts.

End of lab05 for CISC106, Fall 2006 (100 pts)