Starting a New Matlab m.file. Matlab m.files. Matlab m.file Editor/Debugger. The clear all Command. Our Program So Far

Transcription

1 Matlab m.files It is not very convenient to do work directly in the Matlab Command Line Window since: It is hard to remember what we typed. It is hard to edit. It all disappears when we close Matlab. Solution: Use Matlab m.files. Also called or script or program files. We will first re-do the example from lesson 4.2 as a Matlab m.file. We will then add some new features / commands. Starting a New Matlab m.file Go to File = > New => M-file OR Click the New M-file button Matlab m.file Editor/Debugger The Matlab Editor/Debugger will open in a New Window. We will type all our Program Commands in this Window. Any text editor can also be used (but NOT recommended). The Command Window will only be used to Run Programs, Get Answers, Get Help, and Help Debug Programs. The clear all Command As we saw before, to wipe out ALL the memory we use the clear all command. We need clear all the memory each and every time we run a program. We could type the clear all command in the command window every time but that is inefficient. The solution is to put the clear all command as the first executable command in our m.file. Type the following in the Editor Window: clear all We will get to non-executable commands in a few minutes. Enter The Time - Temperature Data As before, we want to create two vectors to store the time and temperature data. As before let s call them time and temp respectively. Type: time = [ ] temp = [ ] in the Editor Window AFTER the clear all command. DO NOT put a semicolon ( ; ) at the end of the time and temp data statements for the time being. Our Program So Far You editor window should like the figure above. Note, the file name appears in the top of the window. Since we have not named the file, the name is Untitled. The asterisk ( * ) after the file name indicates that we have NOT saved the file since our last additions or changes. We will go to File = > Save or Save As to save the file. You can also click the floppy disk icon (button).

2 m.file Naming Rules Syntax: FileName.m The file name can be any combination of letters, numbers, and the underscore ( _ ) character. The FIRST character MUST be a letter. No blank spaces, dashes ( - ) or other non-alphanumeric characters (other than the underscore) are allowed. It is case sensitive (MyFile.m is different than myfile.m). You CANNOT use a Matlab reserved name (e.g., pi, ans, etc.) or Matlab commands (e.g., plot, title, atan, etc.) for the file name. The file extension.m must be part of the name. The Matlab Editor does this automatically. Save and Run Our m.file Save the file to the H:\ drive (your space on the server). Name the file: as4_3.m The editor will automatically add the.m extension. In the Matlab Command Window type:» as4_3 and hit return (DO NOT type the.m extension). Changing the Path Did you get the statement?» as4_3??? Undefined function or variable 'as4_3'. This is because Matlab DID NOT know where to find our file. We need to tell Matlab to look on the H:\ drive. In the Command Window type:» CD H:\ and hit return. Matlab will now look on the H:\ drive first for our file. You must do this EVERY TIME you start Matlab (if your files are stored on the the H:\ drive). Run Our m.file Again Are all your values correct? Did you get the above in the Command Window? All three (3) lines of our program were executed. The time and temp vector definitions were echoed since we did NOT put a semicolons ( ; ) at the end of the lines. Add the Plot to Our Program Edit our file in the Matlab Editor: temp = [ ]; plot(time,temp,'r^'); Click the Floppy Disk Icon in the Editor Window. Run the program again in the Command Window. A Figure Window should open up with the following plot: Add the plot and axis commands. Note the maroon color when both single quotes are used. Now, put a semicolon ( ; ) at the end of all lines. Suppresses echoing of the time and temp data. Not necessary for the other commands but is good practice.

3 Add the Plot Annotation to the Program Edit our file in the Matlab Editor: This is one line. temp = [ ]; plot(time,temp,'r^'); title('coffee Temperature vs Time - Add the title, xlabel, and ylabel commands. Note the maroon color when both single quotes are used. Click the Floppy Disk Icon in the Editor Window. Run the program again in the Command Window. The Figure Window should have the following plot: Modified Example The first cup I used was plastic. I did the experiment again with a ceramic cup. I measured the temperature at the same time intervals I used for the plastic cup (I didn t have to but I did). All the data is on the next slide. I want to keep my first plot as it now appears. I want to add a second plot that includes both sets of data on the same graph. This will require a legend since there will be more than one data set on the same plot. Note, the ceramic cup appears to be a better cup. Temperature of the Coffee in Two Cups as a Function of Time Cup 1 - Plastic Cup 2 - Ceramic Time Temperature Temperature ( minutes ) ( degrees F ) ( degrees F ) We Need To Tell Matlab To: Add the temperature data for the ceramic cup. Keep our current plot for the plastic cup as is. Create a New Plot that contains both sets of data. Set the type and color data marks for the new plot. Set the axes limits & gradations for the new plot. Define the title and axes labels for the new plot. Add a legend to the new plot. Again, developing this short plan is the MOST IMPORTANT step in the entire solution process!!! Editing Matlab m.files Close Matlab! Yes, close Matlab. Closing the Matlab Command Window will close ALL windows. Open Matlab again! Yes, open Matlab again. Open our existing Matlab m.file. Go to File = > Open OR Click the Open File button Go to the the H:\ drive and open the file: as4_3.m

4 Enter The Time - Temperature Data Now we need three (3) vectors to store the time and temperature data for the two cups. We also need to differentiate between the temperature in the plastic cup (cup 1) and the ceramic cup (cup 2). Let s call them time, cup1_temp and cup2_temp. Change the name of temp to cup1_temp. Add the cup2_temp vector. The three data vectors should be as follows: Our Edited Program Since we changed the name of temp to cup1_temp, we need to change the plot command also. Our file in the Matlab Editor should look like: title( Coffee Temperature vs Time - This is one line. Save and Run the Program Click the Floppy Disk Icon in the Editor Window. Notice that the asterisk ( * ) disappears. Run the program again in the Command Window. Type as4_3 and hit return. Did you get the statement?» as4_3??? Undefined function or variable 'as4_3'. Did you add the H:\ drive to your Path? Type CD H:\ in the command window and hit return. Run the program again. Type as4_3 and hit return. Did you get back the original plot? You should have! So Where Are We On Our Plan? Add the temperature data for the ceramic cup. Keep our current plot for the plastic cup as is. Create a New Plot that contains both sets of data. Set the type and color data marks for the new plot. Set the axes limits & gradations for the new plot. Define the title and axes labels for the new plot. Add a legend to the new plot. Maybe the Help File on plot will be helpful!! Maybe the Help File on 2-D graphs will be helpful!! Looks like we need the axis, title, xlabel, and ylabel commands again. Go to the Help File on plot The syntax to get two or more data sets is: vector of independent variable values for data set 1 vector of dependent variable values for data set 1 format code for data set 1 vector of independent variable values for data set 2 vector of dependent variable values for data set 2 format code for data set 2 etc. Add the Second plot Command to Our Program In our case both data sets use the same vector of independent variable values (i.e., the vector time). This is NOT necessary in general. We could have made our temperature measurements at different times for the two cups if we wanted. Plot the cup 1 data using blue triangles. Plot the cup 2 data using red circles. Therefore, we need to add the following command at the end of our program:

5 Our Edited Program Our file in the Matlab Editor should look like: title( Coffee Temperature vs Time - The Figure Window should now look like the following: Any Problems? Obviously: We need to adjust the axes scales. We need to add the title and axes labels. We need to add a legend. What happened to our first plot? The second plot command overwrote the first plot command. (and we then also lost all the axis, title, xlabel, and ylabel information). We need to tell Matlab to plot the two plots in separate windows! How do we do this? It is not real obvious and a little difficult to find in the Help File. Handle Graphics Matlab refers to all general graphics items as Handle Graphics. Open the Help Window: Double Click Here More on Handle Graphics The figure Command We want to look at these two commands. We will look at some of these commands in the near future. In English, the figure(h) command: Opens a new figure window numbered H if that figure window is NOT already opened. Activates the figure window numbered H if that figure window IS already opened. Either way, ALL plotting commands will appear in the figure window numbered H until the next figure command is given.

6 The clf reset Command In English, the clf reset command: Clears and resets all parameters (title, plot, etc.) of the active figure window. Should appear after every figure(h) command. Let s edit our program file. Our file in the Matlab Editor should look like: figure(1); clf reset Add these lines. title( Coffee Temperature vs Time - figure(2); clf reset; Two Figure Windows should now look like the following: You have to move figure 2 to see figure 1 Clean up the Second Plot Edit our file in the Matlab Editor: figure(2); clf reset; title('coffee Temperatures vs Time - The rest of the code is NOT shown. This is one line. Add the axis, title, xlabel, and ylabel commands. We can use the same axes limits Note the slight change in the title. Figure Window 2 should now look like the following: We need a legend! Go to the help file. Key Statements

7 The legend Command The legend command syntax: This is one line. legend('text for 1st data','text for 2nd data',,position on plot); The text can be anything we want but should be short. The order of text descriptions MUST be the same as the order of the data sets we plotted. For position it is best to use 0 (zero) so we can move the legend where we want it. Add the following line after the ylabel command for the second plot: legend('cup1 - Plastic','Cup 2 - Ceramic',0); Figure Window 2 should now look like the following: Try moving the legend around with the mouse. % - The Comment Operator If Matlab sees a % (percent sign) it ignores the rest of the line. The exception is if the % is inside a command. Therefore, we can use this % to add "comments" to our programs. Comments are used to tell the reader what is going on in the program at various points. The Comment Operator is a non-executable command and can appear BEFORE the clear all command. Undocumented or Poorly Documented program are Unacceptable!!! Examples of the comment operator: % Clear all memory % Enter time and temperature data. % Activate figure 1 and clear all parameters. figure(1); clf reset; % Create plot 1 and set axes limits. The blank lines make it more readable. Notice, the comments are always green. Our Standard header We will use a standard header the contains: A place for your section name, date, and name. A brief program description. A listing and brief description of all variables The standard header is available on the web site. Download the header to your file area on the H:\ drive. Open the header using the Matlab Editor. Use Cut and Paste to insert the header into your program. Edit as needed. See examples on the web site. Matlab Homework Format All homework will follow the required format: Cover page - handwritten. DOCUMENTED m.file. PROPER plots and other formatted output as required. Assumptions, discussions, further calculations, etc. as required. All m.files will include: Standard header. Appropriate number of in-line comments. End of program statement. See web site for examples.