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8.11: Editing Files and Creating Functions (PC)

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    You should write a MATLAB program whenever you anticipate executing some sequence of statements several times or again in a later session. On an IBM PC, you may use any text editor to write a program, as long as the file can be saved in ASCII format without the control codes used by most word processors. Applicable text editors include Edix, Wordstar, XTree Pro, and Turbo Pascal's editor.

    Editing Files

    If you have enough memory, you can run your editor without leaving MATLAB by using the exclamation point (!), like this:

    ≫ !EDIX

    The exclamation point may be used to execute any DOS command or program from MATLAB. When the command or program finishes, your MATLAB variables are just as you left them. Use your editor to write program lines just as you would type them in MATLAB's command mode. Then save the file with extension .m in the directory where you will run MATLAB. Such MATLAB programs are called m-files. You may run your m-file by typing the file name (without the .m extension) at the MATLAB command prompt (\(\gg\)).

    Script Files

    There are two kinds of m-files, called script files and functions. Running a script file is exactly like typing the commands it contains at the \(\gg\) prompt. Your m-file will automatically be a script file unless you specify otherwise, as described later. Practice by entering, saving, and running plotsin.m as listed next:

    t = -6:.2:6;
    y = sin(t);

    When the pause is executed, you will need to press a key to go on. If you type whos after running plotsin, you will see that the variables t and y remain in memory. Comments are important to a script file. They are marked with the symbol %. Anything following this symbol on a line is assumed to be a comment and is ignored by the MATLAB program interpreter.


    Functions differ from script files in that they have designated input and output variables. Any other variables used within a function are local variables, which do not remain after the function terminates and which have no effect on variables outside the function. Many of the functions supplied with MATLAB are actually m-files. A good example is triu.m:

    ≫ type triu

    The word function at the beginning of the file makes it a function rather than a script file. The function name in this line must match the file name. The input variables of triu are x and k, meaning that the first input argument will be referred to as x and the second as k within the function. Likewise, the function line designates y as the output. There is nothing special about the variable names x,k, and y when the function is used. It is only that whatever inputs and output you use will be referred to as x,k, and y inside the function. The variables m,n,j, and i are created temporarily when triu runs and disappear when it terminates. They are local variables and have no effect on variables with the same names outside the function. In contrast, a script file has no local variables and does no substitution of input and output variable names.

    As an exercise, enter and save the function perp.m:

       function y=perp(x)
          % PERP(x) is a complex number perpendicular to x.
          j = sqrt(-1);
          y = j*real(x)-imag(x);

    Evaluate perp on various complex numbers. Replace the last line by y = x*j;. Do you get the same result? Why?

    Printing Files and Graphics

    To display an m-file on the screen, use the instruction ≫ type filename. To make a copy at a printer, use the DOS command ≫ !print filename.m. Graphics hardcopy is available through the commands meta and gpp. See the MATLAB manual for more information.

    This page titled 8.11: Editing Files and Creating Functions (PC) is shared under a CC BY 3.0 license and was authored, remixed, and/or curated by Louis Scharf (OpenStax CNX) via source content that was edited to the style and standards of the LibreTexts platform; a detailed edit history is available upon request.