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<span id="Multiple-Return-Values"></span><div class="header">
<p>
Next: <a href="Variable_002dlength-Return-Lists.html" accesskey="n" rel="next">Variable-length Return Lists</a>, Previous: <a href="Returning-from-a-Function.html" accesskey="p" rel="prev">Returning from a Function</a>, Up: <a href="Functions-and-Scripts.html" accesskey="u" rel="up">Functions and Scripts</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html" title="Index" rel="index">Index</a>]</p>
</div>
<hr>
<span id="Multiple-Return-Values-1"></span><h3 class="section">11.4 Multiple Return Values</h3>
<p>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
</p>
<div class="example">
<pre class="example">function [<var>ret-list</var>] = <var>name</var> (<var>arg-list</var>)
<var>body</var>
endfunction
</pre></div>
<p>where <var>name</var>, <var>arg-list</var>, and <var>body</var> have the same meaning
as before, and <var>ret-list</var> 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 <var>ret-list</var> has
only one element, this form of the <code>function</code> statement is
equivalent to the form described in the previous section.
</p>
<p>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.
</p>
<div class="example">
<pre class="example">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
</pre></div>
<p>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.
</p>
<p>It is possible to use the <code>nthargout</code> function to obtain only some
of the return values or several at once in a cell array.
See <a href="Cell-Array-Objects.html">Cell Array Objects</a>.
</p>
<span id="XREFnthargout"></span><dl>
<dt id="index-nthargout">: <em></em> <strong>nthargout</strong> <em>(<var>n</var>, <var>func</var>, …)</em></dt>
<dt id="index-nthargout-1">: <em></em> <strong>nthargout</strong> <em>(<var>n</var>, <var>ntot</var>, <var>func</var>, …)</em></dt>
<dd><p>Return the <var>n</var>th output argument of the function specified by the
function handle or string <var>func</var>.
</p>
<p>Any additional arguments are passed directly to <var>func</var>. The total
number of arguments to call <var>func</var> with can be passed in <var>ntot</var>; by
default <var>ntot</var> is <var>n</var>. The input <var>n</var> can also be a vector of
indices of the output, in which case the output will be a cell array of the
requested output arguments.
</p>
<p>The intended use <code>nthargout</code> is to avoid intermediate variables. For
example, when finding the indices of the maximum entry of a matrix, the
following two compositions of nthargout
</p>
<div class="example">
<pre class="example"><var>m</var> = magic (5);
cell2mat (nthargout ([1, 2], @ind2sub, size (<var>m</var>),
nthargout (2, @max, <var>m</var>(:))))
⇒ 5 3
</pre></div>
<p>are completely equivalent to the following lines:
</p>
<div class="example">
<pre class="example"><var>m</var> = magic (5);
[~, idx] = max (<var>M</var>(:));
[i, j] = ind2sub (size (<var>m</var>), idx);
[i, j]
⇒ 5 3
</pre></div>
<p>It can also be helpful to have all output arguments in a single cell in the
following manner:
</p>
<div class="example">
<pre class="example"><var>USV</var> = nthargout ([1:3], @svd, hilb (5));
</pre></div>
<p><strong>See also:</strong> <a href="Defining-Functions.html#XREFnargin">nargin</a>, <a href="#XREFnargout">nargout</a>, <a href="Variable_002dlength-Argument-Lists.html#XREFvarargin">varargin</a>, <a href="Variable_002dlength-Return-Lists.html#XREFvarargout">varargout</a>, <a href="Ignoring-Arguments.html#XREFisargout">isargout</a>.
</p></dd></dl>
<p>In addition to setting <code>nargin</code> each time a function is called,
Octave also automatically initializes <code>nargout</code> 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
built-in variable <code>ans</code> does not figure in the count of output
arguments, so the value of <code>nargout</code> may be zero.
</p>
<p>The <code>svd</code> and <code>lu</code> functions are examples of built-in
functions that behave differently depending on the value of
<code>nargout</code>.
</p>
<p>It is possible to write functions that only set some return values. For
example, calling the function
</p>
<div class="example">
<pre class="example">function [x, y, z] = f ()
x = 1;
z = 2;
endfunction
</pre></div>
<p>as
</p>
<div class="example">
<pre class="example">[a, b, c] = f ()
</pre></div>
<p>produces:
</p>
<div class="example">
<pre class="example">a = 1
b = [](0x0)
c = 2
</pre></div>
<p>along with a warning.
</p>
<span id="XREFnargout"></span><dl>
<dt id="index-nargout">: <em></em> <strong>nargout</strong> <em>()</em></dt>
<dt id="index-nargout-1">: <em></em> <strong>nargout</strong> <em>(<var>fcn</var>)</em></dt>
<dd><p>Report the number of output arguments from a function.
</p>
<p>Called from within a function, return the number of values the caller
expects to receive. At the top level, <code>nargout</code> with no argument is
undefined and will produce an error.
</p>
<p>If called with the optional argument <var>fcn</var>—a function name or
handle—return the number of declared output values that the function can
produce.
</p>
<p>If the final output argument is <var>varargout</var> the returned value is
negative.
</p>
<p>For example,
</p>
<div class="example">
<pre class="example">f ()
</pre></div>
<p>will cause <code>nargout</code> to return 0 inside the function <code>f</code> and
</p>
<div class="example">
<pre class="example">[s, t] = f ()
</pre></div>
<p>will cause <code>nargout</code> to return 2 inside the function <code>f</code>.
</p>
<p>In the second usage,
</p>
<div class="example">
<pre class="example">nargout (@histc) # or nargout ("histc") using a string input
</pre></div>
<p>will return 2, because <code>histc</code> has two outputs, whereas
</p>
<div class="example">
<pre class="example">nargout (@imread)
</pre></div>
<p>will return -2, because <code>imread</code> has two outputs and the second is
<var>varargout</var>.
</p>
<p>Programming Note. <code>nargout</code> does not work for built-in functions and
returns -1 for all anonymous functions.
</p>
<p><strong>See also:</strong> <a href="Defining-Functions.html#XREFnargin">nargin</a>, <a href="Variable_002dlength-Return-Lists.html#XREFvarargout">varargout</a>, <a href="Ignoring-Arguments.html#XREFisargout">isargout</a>, <a href="#XREFnthargout">nthargout</a>.
</p></dd></dl>
<hr>
<div class="header">
<p>
Next: <a href="Variable_002dlength-Return-Lists.html" accesskey="n" rel="next">Variable-length Return Lists</a>, Previous: <a href="Returning-from-a-Function.html" accesskey="p" rel="prev">Returning from a Function</a>, Up: <a href="Functions-and-Scripts.html" accesskey="u" rel="up">Functions and Scripts</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html" title="Index" rel="index">Index</a>]</p>
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