Graphics Programs Reference
In-Depth Information
statement, which identifies the file as a function M-file. The first line specifies
the name of the function and describes both its input arguments (or parame-
ters) and its output values. In this example, the function is called
sinelimit
.
The file name and the function name should match.
The function
sinelimit
takes one input argument and returns one out-
put value, called
c
and
y
(respectively) inside the M-file. When the function
finishesexecuting,itsoutputwillbeassignedto
ans
(bydefault)ortoanyother
variable you choose, just as with a built-in function. The remaining lines of
the M-file define the function. In this example,
b
is a row vector consisting
of the integers from
1
to
c
. The vector
y
contains the results of computing
sin(
x
)
/
x
where
x
=
10
−
b
; the prime makes
y
a column vector. Notice that the
output of the lines defining
b
,
x
, and
y
is suppressed witha semicolon. In
general, the output of intermediate calculations in a function M-file should be
suppressed.
Of course, when we run the M-file above, we do want to see the results of
the last line of the file, so a natural impulse would be to avoid putting a
semicolon on this last line. But because this is a function M-file, running it
will automatically display the contents of the designated output variable
y
.
Thus if we did not put a semicolon at the end of the last line, we would see
the same numbers twice when we run the function!
Note that the variables used in a function M-file, such as
b
,
x
, and
y
in
sinelimit.m
, are
local variables
. This means that, unlike the variables that
are defined in a script M-file, these variables are completely unrelated to any
variables with the same names that you may have used in the Command
Window, and MATLABdoes not remember their values after the function
M-file is executed. For further information, see the section
Variables in
Function M-files
in Chapter 4.
Here is an example that shows how to use the function
sinelimit
:
>> sinelimit(5)
ans =
0.99833416646828
0.99998333341667
0.99999983333334
0.99999999833333
0.99999999998333
None of the values of
b
from 1 to 5 yields the desired answer, 1, to 15 digits.
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