Unlike many other computer languages, Octave allows you to define functions that return more than one value. The syntax for defining functions that return multiple values is
function [ret-list] = name (arg-list) body endfunction
where name, arg-list, and body have the same meaning
as before, and ret-list is a comma-separated list of variable
names that will hold the values returned from the function. The list of
return values must have at least one element. If ret-list has
only one element, this form of the
function statement is
equivalent to the form described in the previous section.
Here is an example of a function that returns two values, the maximum element of a vector and the index of its first occurrence in the vector.
function [max, idx] = vmax (v) idx = 1; max = v (idx); for i = 2:length (v) if (v (i) > max) max = v (i); idx = i; endif endfor endfunction
In this particular case, the two values could have been returned as elements of a single array, but that is not always possible or convenient. The values to be returned may not have compatible dimensions, and it is often desirable to give the individual return values distinct names.
In addition to setting
nargin each time a function is called,
Octave also automatically initializes
nargout to the number of
values that are expected to be returned. This allows you to write
functions that behave differently depending on the number of values that
the user of the function has requested. The implicit assignment to the
ans does not figure in the count of output
arguments, so the value of
nargout may be zero.
lu functions are examples of built-in
functions that behave differently depending on the value of
It is possible to write functions that only set some return values. For example, calling the function
function [x, y, z] = f () x = 1; z = 2; endfunction
[a, b, c] = f ()
a = 1 b = (0x0) c = 2
along with a warning if the value of the built-in variable
warn_undefined_return_values is nonzero.
Within a function, return the number of values the caller expects to receive. If called with the optional argument fcn_name, return the maximum number of values the named function can produce, or -1 if the function can produce a variable number of values.
For example,f ()
nargoutto return 0 inside the function
fand[s, t] = f ()
nargoutto return 2 inside the function
At the top level,
If the value of
warn_undefined_return_valuesis nonzero, print a warning if a function does not define all the values in the return list which are expected. The default value is 1.
If n is in the range nargin_min through nargin_max inclusive, return the empty matrix. Otherwise, return a message indicating whether n is too large or too small.
This is useful for checking to see that the number of arguments supplied to a function is within an acceptable range.