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Unformatted text preview: Chapter 3 Programming in Matlab 3.1 ME 218 Lab: Programming Structures in MATLAB The simpliest programs execute the first line, the second line, the third line and so on. But when we use programming structures (i.e. FOR loops, WHILE loops, and IF statements, we can cause the program to repeat certain steps (lines in a program), or skip steps. Stuctures control the flow of computer programs somewhat like traffic signs control the motion of cars. 3.1.1 Create, Name, and Save an mfile In MATLAB, open up a new mfile. At the top of your mfile, type your name, todays date, and the name of this exersize as follows: % Billy Bob % July 4, 1776 % ME 218 Lab:Programming Structures in MATLAB 35 CHAPTER 3. PROGRAMMING IN MATLAB 36 MATLAB ignores everything to the right of the % symbol. In this way, you can type comment to yourself or others within a MATLAB program without affecting the program. This is a good idea. Before we proceed, go ahead and save you mfile. Call it structures.m 3.1.2 FOR Loops You can give MATLAB a vector and a variable name and have it execute a list of commands with the variable set to each entry of the vector, one at a time. In words, here is how: for variable = vector instructions to be repeated end MATLAB assigns a variable (called the counting variable) to be the first entry of the vector and runs the instructions to be repeated. Then, MATLAB will move to the next entry in the vector, assign that value to the vector, and run the instructions again. Type this example into your mfile: clear for x = [ 1 3 5 ] x end Notice that we started out with the clear command which erases any previously stored variables in MATLAB. We also indented the line within the for loopthis is a good idea because it makes the program easier to read. If we have more than one line between the for and the end statements, we would have indented them all. Now, save and then run your MATLAB file (click the Run button or select Run from the Debug menu). MATLAB should print out the value of x three times in the Command Window. Each time, x has been changed to an entry of the vector in the for command. Your result should look like this: MATLAB response: x = 1 x = 3 x = 5 You can also use the range notation (:) to generate a vector for the for loop: for x = 1:2:5 x end CHAPTER 3. PROGRAMMING IN MATLAB 37 will produce the same results as the previous example. Problem 3.1 Enter the following commands in your mfile and run it if myValue equals 9. What size is y and what will be in each entry of y ? n = myValue; for x = 1:n y(x) = exp(x) ; end y Now, type whos in the Command Window to see what is left behind after running the for loop and assuming myValue equals 10: whos MATLAB response: Name Size Bytes Class ==== ==== ===== ===== x 1 1 8 double array y 1 10 80 double array Note that x is just a scalar! If you want x to hold the vector of all the values that the instructions were evaluated with, then you need to define it before hand:...
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This note was uploaded on 12/14/2011 for the course ME 218 taught by Professor Unknown during the Fall '08 term at University of Texas at Austin.
 Fall '08
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