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More about M-Files 57

If you have not previously defined u, then typing scriptex2 will produce an
error message. However, if you type scriptex2 after running scriptex1,
then the definition of u from the first script will be used in the second script
and the output n=4 will be displayed.
If you don’t want the output of a script M-file to depend on any earlier compu-
tations in your MATLAB session, put the line clear all near the beginning
of the M-file, as we suggested in Structuring Script M-files in Chapter 3.

Variables in Function M-Files

The variables used in a function M-file are local, meaning that they are un-
affected by, and have no effect on, the variables in your Workspace. Consider
the following function M-file, called sq.m:

function z = sq(x)
% sq(x) returns the square of x.
z = x.ˆ2;

Typing sq(3) produces the answer 9, whether or not x or z is already defined
in your Workspace, and neither defines them, nor changes their definitions, if
they have been previously defined.

Structure of Function M-Files
The first line in a function M-file is called the function definition line; it defines
the function name, as well as the number and order of input and output argu-
ments. Following the function definition line, there can be several comment
lines that begin with a percent sign (%). These lines are called help text and
are displayed in response to the command help. In the M-file sq.m above,
there is only one line of help text; it is displayed when you type help sq.
The remaining lines constitute the function body; they contain the MATLAB
statements that calculate the function values. In addition, there can be com-
ment lines (lines beginning with %) anywhere in an M-file. All statements in
a function M-file that normally produce output should end with a semicolon
to suppress the output.
Function M-files can have multiple input and output arguments. Here is
an example, called polarcoordinates.m, withtwo input and two output
arguments:

function [r, theta] = polarcoordinates(x, y)
% polarcoordinates(x, y) returns the polar coordinates
% of the point with rectangular coordinates (x, y).