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When you write a MATLAB® function or script, you save it to a file called an M-file (named after its .m file extension). There are two types of M-files that you can write: scripts and functions. This section covers basic program development, describes how to write and call scripts and functions, and shows how to pass different types of data in a function call. Associated with each step of this process are certain MATLAB tools and utilities that are fully documented in the Desktop Tools and Development Environment documentation.
For more ideas on good programming style, see Program Development in the MATLAB Programming Tips documentation. The Programming Tips section is a compilation of useful pieces of information that can show you alternate and often more efficient ways to accomplish common programming tasks while also expanding your knowledge of MATLAB.
You can type in your program code using any text editor. This section focuses on using the MATLAB Editor/Debugger for this purpose. The Editor/Debugger is fully documented in Ways to Edit and Debug Files in the Desktop Tools and Development Environment documentation.
The first step in creating a program is to open an editing window. To create a new M-file, type the word edit at the MATLAB command prompt. To edit an existing M-file, type edit followed by the filename:
edit drawPlot.m
MATLAB opens a new window for entering your program code. As you type in your program, MATLAB keeps track of the line numbers in the left column.
It is usually a good idea to save your program periodically while you are in the development process. To do this, click File > Save in the Editor/Debugger. Enter a filename with a .m extension in the Save file as dialog box that appears and click OK. It is customary and less confusing if you give the M-file the same name as the first function in the M-file.
Before trying to run your program, make sure that its M-file is on the MATLAB path. The MATLAB path defines those directories that you want MATLAB to know about when executing M-files. The path includes all the directories that contain functions provided with MATLAB. It should also include any directories that you use for your own functions.
Use the which function to see if your program is on the path:
which drawPlot D:\matlabR14\work\drawPlot.m
If not, add its directory to the path using the addpath function:
addpath('D:\matlabR14\work')
Now you can run the program just by typing the name of the M-file at the MATLAB command prompt:
drawPlot(xdata, ydata)
In all but the simplest programs, you are likely to encounter some type of unexpected behavior when you run the program for the first time. Program defects can show up in the form of warning or error messages displayed in the command window, programs that hang (never terminate), inaccurate results, or some number of other symptoms. This is where the second functionality of the MATLAB Editor/Debugger becomes useful.
The MATLAB Debugger enables you to examine the inner workings of your program while you run it. You can stop the execution of your program at any point and then continue from that point, stepping through the code line by line and examining the results of each operation performed. You have the choice of operating the debugger from the Editor window that displays your program, from the MATLAB command line, or both.
You can step through the program right from the start if you want. For longer programs, you will probably save time by stopping the program somewhere in the middle and stepping through from there. You can do this by approximating where the program code breaks and setting a stopping point (or breakpoint) at that line. Once a breakpoint has been set, start your program from the MATLAB command prompt. MATLAB opens an Editor/Debugger window (if it is not already open) showing a green arrow pointing to the next line to execute.
From this point, you can examine any values passed into the program, or the results of each operation performed. You can step through the program line by line to see which path is taken and why. You can step into any functions that your program calls, or choose to step over them and just see the end results. You can also modify the values assigned to a variable and see how that affects the outcome.
To learn about using the MATLAB Debugger, see Debugging and Improving M-Files in the Desktop Tools and Development Environment documentation. Type help debug for a listing of all MATLAB debug functions.
For programming tips on how to debug, see Debugging.
Even after your program is bug-free, there are still some steps you can take to improve its performance and readability. The MATLAB M-Lint utility generates a report that can highlight potential problems in your code. For example, you may be using the elementwise AND operator (&) where the short-circuit AND (&&) is more appropriate. You may be using the find function in a context where logical subscripting would be faster.
MATLAB offers M-Lint and several other reporting utilities to help you make the finishing touches to your program code. These tools are described under Tuning and Refining M-Files in the Desktop Tools and Development Environment documentation.
The MATLAB Profiler generates a report that shows how your program spends its processing time. For details about using the MATLAB Profiler, see Profiling for Improving Performance in the MATLAB Desktop Tools and Development Environment documentation. For tips on other ways to improve the performance of your programs, see Performance.
Three types of reports are available:
The summary report provides performance information on your main program and on every function it calls. This includes how many times each function is called, the total time spent in that function, along with a bar graph showing the relative time spent by each function.
When you click a function name in the summary report, MATLAB displays a detailed report on that function. This report shows the lines of that function that take up the most time, the time spent executing that line, the percentage of total time for that function that is spent on that line, and a bar graph showing the relative time spent on the line.
The detail report for a function also displays the entire M-file code for that function. This listing enables you to view the time-consuming code in the context of the entire function body. For every line of code that takes any significant time, additional performance information is provided by the statistics and by the color and degree of highlighting of the program code.
Source control systems offer a way to manage large numbers of files while they are under development. They keep track of the work done on these files as your project progresses, and also ensure that changes are made in a secure and orderly fashion.
If you have a source control system available to you, you will probably want to check your M-files into the system once they are complete. If further work is required on one of those files, you just check it back out, make the necessary modifications, and then check it back in again.
MATLAB provides an interface to external source control systems so that you can check files in and out directly from your MATLAB session. See Revision Control in the Desktop Tools and Development Environment documentation for instructions on how to use this interface.
| Functions and Scripts | Working with M-Files | |
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