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<a name="Multiple-Return-Values"></a>
<div class="header">
<p>
Next: <a href="Variable_002dlength-Argument-Lists.html#Variable_002dlength-Argument-Lists" accesskey="n" rel="next">Variable-length Argument Lists</a>, Previous: <a href="Defining-Functions.html#Defining-Functions" accesskey="p" rel="prev">Defining Functions</a>, Up: <a href="Functions-and-Scripts.html#Functions-and-Scripts" accesskey="u" rel="up">Functions and Scripts</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
</div>
<hr>
<a name="Multiple-Return-Values-1"></a>
<h3 class="section">11.3 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) &gt; 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">Cell Array Objects</a>.
</p>
<a name="XREFnthargout"></a><dl>
<dt><a name="index-nthargout"></a>Function File: <em></em> <strong>nthargout</strong> <em>(<var>n</var>, <var>func</var>, &hellip;)</em></dt>
<dt><a name="index-nthargout-1"></a>Function File: <em></em> <strong>nthargout</strong> <em>(<var>n</var>, <var>ntot</var>, <var>func</var>, &hellip;)</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>(:))))
&rArr; 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]
&rArr; 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="#XREFvarargin">varargin</a>, <a href="#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>
<a name="XREFnargout"></a><dl>
<dt><a name="index-nargout"></a>Built-in Function: <em></em> <strong>nargout</strong> <em>()</em></dt>
<dt><a name="index-nargout-1"></a>Built-in Function: <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>&mdash;a function name or
handle&mdash;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 (&quot;histc&quot;)
</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="#XREFvarargout">varargout</a>, <a href="Ignoring-Arguments.html#XREFisargout">isargout</a>, <a href="#XREFnthargout">nthargout</a>.
</p></dd></dl>


<p>It is good practice at the head of a function to verify that it has been called
correctly.  In Octave the following idiom is seen frequently
</p>
<div class="example">
<pre class="example">if (nargin &lt; min_#_inputs || nargin &gt; max_#_inputs)
  print_usage ();
endif
</pre></div>

<p>which stops the function execution and prints a message about the correct
way to call the function whenever the number of inputs is wrong.
</p>
<p>For compatibility with <small>MATLAB</small>, <code>narginchk</code> and <code>nargoutchk</code> are
available which provide similar error checking.
</p>
<a name="XREFnarginchk"></a><dl>
<dt><a name="index-narginchk"></a>Function File: <em></em> <strong>narginchk</strong> <em>(<var>minargs</var>, <var>maxargs</var>)</em></dt>
<dd><p>Check for correct number of input arguments.
</p>
<p>Generate an error message if the number of arguments in the calling function
is outside the range <var>minargs</var> and <var>maxargs</var>.  Otherwise, do nothing.
</p>
<p>Both <var>minargs</var> and <var>maxargs</var> must be scalar numeric values.  Zero,
Inf, and negative values are all allowed, and <var>minargs</var> and <var>maxargs</var>
may be equal.
</p>
<p>Note that this function evaluates <code>nargin</code> on the caller.
</p>

<p><strong>See also:</strong> <a href="#XREFnargoutchk">nargoutchk</a>, <a href="Raising-Errors.html#XREFerror">error</a>, <a href="#XREFnargout">nargout</a>, <a href="Defining-Functions.html#XREFnargin">nargin</a>.
</p></dd></dl>


<a name="XREFnargoutchk"></a><dl>
<dt><a name="index-nargoutchk"></a>Function File: <em></em> <strong>nargoutchk</strong> <em>(<var>minargs</var>, <var>maxargs</var>)</em></dt>
<dt><a name="index-nargoutchk-1"></a>Function File: <em><var>msgstr</var> =</em> <strong>nargoutchk</strong> <em>(<var>minargs</var>, <var>maxargs</var>, <var>nargs</var>)</em></dt>
<dt><a name="index-nargoutchk-2"></a>Function File: <em><var>msgstr</var> =</em> <strong>nargoutchk</strong> <em>(<var>minargs</var>, <var>maxargs</var>, <var>nargs</var>, &quot;string&quot;)</em></dt>
<dt><a name="index-nargoutchk-3"></a>Function File: <em><var>msgstruct</var> =</em> <strong>nargoutchk</strong> <em>(<var>minargs</var>, <var>maxargs</var>, <var>nargs</var>, &quot;struct&quot;)</em></dt>
<dd><p>Check for correct number of output arguments.
</p>
<p>In the first form, return an error if the number of arguments is not between
<var>minargs</var> and <var>maxargs</var>.  Otherwise, do nothing.  Note that this
function evaluates the value of <code>nargout</code> on the caller so its value
must have not been tampered with.
</p>
<p>Both <var>minargs</var> and <var>maxargs</var> must be numeric scalars.  Zero, Inf,
and negative are all valid, and they can have the same value.
</p>
<p>For backwards compatibility, the other forms return an appropriate error
message string (or structure) if the number of outputs requested is
invalid.
</p>
<p>This is useful for checking to that the number of output arguments supplied
to a function is within an acceptable range.
</p>
<p><strong>See also:</strong> <a href="#XREFnarginchk">narginchk</a>, <a href="Raising-Errors.html#XREFerror">error</a>, <a href="#XREFnargout">nargout</a>, <a href="Defining-Functions.html#XREFnargin">nargin</a>.
</p></dd></dl>


<p>Besides the number of arguments, inputs can be checked for various properties.
<code>validatestring</code> is used for string arguments and
<code>validateattributes</code> for numeric arguments.
</p>
<a name="XREFvalidatestring"></a><dl>
<dt><a name="index-validatestring"></a>Function File: <em><var>validstr</var> =</em> <strong>validatestring</strong> <em>(<var>str</var>, <var>strarray</var>)</em></dt>
<dt><a name="index-validatestring-1"></a>Function File: <em><var>validstr</var> =</em> <strong>validatestring</strong> <em>(<var>str</var>, <var>strarray</var>, <var>funcname</var>)</em></dt>
<dt><a name="index-validatestring-2"></a>Function File: <em><var>validstr</var> =</em> <strong>validatestring</strong> <em>(<var>str</var>, <var>strarray</var>, <var>funcname</var>, <var>varname</var>)</em></dt>
<dt><a name="index-validatestring-3"></a>Function File: <em><var>validstr</var> =</em> <strong>validatestring</strong> <em>(&hellip;, <var>position</var>)</em></dt>
<dd><p>Verify that <var>str</var> is an element, or substring of an element, in
<var>strarray</var>.
</p>
<p>When <var>str</var> is a character string to be tested, and <var>strarray</var> is a
cellstr of valid values, then <var>validstr</var> will be the validated form
of <var>str</var> where validation is defined as <var>str</var> being a member
or substring of <var>validstr</var>.  This is useful for both verifying
and expanding short options, such as <code>&quot;r&quot;</code>, to their longer forms,
such as <code>&quot;red&quot;</code>.  If <var>str</var> is a substring of <var>validstr</var>, and
there are multiple matches, the shortest match will be returned if all
matches are substrings of each other.  Otherwise, an error will be raised
because the expansion of <var>str</var> is ambiguous.  All comparisons are case
insensitive.
</p>
<p>The additional inputs <var>funcname</var>, <var>varname</var>, and <var>position</var>
are optional and will make any generated validation error message more
specific.
</p>
<p>Examples:
</p>
<div class="smallexample">
<pre class="smallexample">validatestring (&quot;r&quot;, {&quot;red&quot;, &quot;green&quot;, &quot;blue&quot;})
&rArr; &quot;red&quot;

validatestring (&quot;b&quot;, {&quot;red&quot;, &quot;green&quot;, &quot;blue&quot;, &quot;black&quot;})
&rArr; error: validatestring: multiple unique matches were found for 'b':
   blue, black
</pre></div>


<p><strong>See also:</strong> <a href="Comparing-Strings.html#XREFstrcmp">strcmp</a>, <a href="Comparing-Strings.html#XREFstrcmpi">strcmpi</a>, <a href="#XREFvalidateattributes">validateattributes</a>, <a href="#XREFinputParser">inputParser</a>.
</p></dd></dl>


<a name="XREFvalidateattributes"></a><dl>
<dt><a name="index-validateattributes"></a>Function File: <em></em> <strong>validateattributes</strong> <em>(<var>A</var>, <var>classes</var>, <var>attributes</var>)</em></dt>
<dt><a name="index-validateattributes-1"></a>Function File: <em></em> <strong>validateattributes</strong> <em>(<var>A</var>, <var>classes</var>, <var>attributes</var>, <var>arg_idx</var>)</em></dt>
<dt><a name="index-validateattributes-2"></a>Function File: <em></em> <strong>validateattributes</strong> <em>(<var>A</var>, <var>classes</var>, <var>attributes</var>, <var>func_name</var>)</em></dt>
<dt><a name="index-validateattributes-3"></a>Function File: <em></em> <strong>validateattributes</strong> <em>(<var>A</var>, <var>classes</var>, <var>attributes</var>, <var>func_name</var>, <var>arg_name</var>)</em></dt>
<dt><a name="index-validateattributes-4"></a>Function File: <em></em> <strong>validateattributes</strong> <em>(<var>A</var>, <var>classes</var>, <var>attributes</var>, <var>func_name</var>, <var>arg_name</var>, <var>arg_idx</var>)</em></dt>
<dd><p>Check validity of input argument.
</p>
<p>Confirms that the argument <var>A</var> is valid by belonging to one of
<var>classes</var>, and holding all of the <var>attributes</var>.  If it does not,
an error is thrown, with a message formatted accordingly.  The error
message can be made further complete by the function name <var>fun_name</var>,
the argument name <var>arg_name</var>, and its position in the input
<var>arg_idx</var>.
</p>
<p><var>classes</var> must be a cell array of strings (an empty cell array is
allowed) with the name of classes (remember that a class name is case
sensitive).  In addition to the class name, the following categories
names are also valid:
</p>
<dl compact="compact">
<dt><code>&quot;float&quot;</code></dt>
<dd><p>Floating point value comprising classes <code>&quot;double&quot;</code> and
<code>&quot;single&quot;</code>.
</p>
</dd>
<dt><code>&quot;integer&quot;</code></dt>
<dd><p>Integer value comprising classes (u)int8, (u)int16, (u)int32, (u)int64.
</p>
</dd>
<dt><code>&quot;numeric&quot;</code></dt>
<dd><p>Numeric value comprising either a floating point or integer value.
</p>
</dd>
</dl>

<p><var>attributes</var> must be a cell array with names of checks for <var>A</var>.
Some of them require an additional value to be supplied right after the
name (see details for each below).
</p>
<dl compact="compact">
<dt><code>&quot;&lt;=&quot;</code></dt>
<dd><p>All values are less than or equal to the following value in <var>attributes</var>.
</p>
</dd>
<dt><code>&quot;&lt;&quot;</code></dt>
<dd><p>All values are less than the following value in <var>attributes</var>.
</p>
</dd>
<dt><code>&quot;&gt;=&quot;</code></dt>
<dd><p>All values are greater than or equal to the following value in
<var>attributes</var>.
</p>
</dd>
<dt><code>&quot;&gt;&quot;</code></dt>
<dd><p>All values are greater than the following value in <var>attributes</var>.
</p>
</dd>
<dt><code>&quot;2d&quot;</code></dt>
<dd><p>A 2-dimensional matrix.  Note that vectors and empty matrices have
2 dimensions, one of them being of length 1, or both length 0.
</p>
</dd>
<dt><code>&quot;3d&quot;</code></dt>
<dd><p>Has no more than 3 dimensions.  A 2-dimensional matrix is a 3-D matrix
whose 3rd dimension is of length 1.
</p>
</dd>
<dt><code>&quot;binary&quot;</code></dt>
<dd><p>All values are either 1 or 0.
</p>
</dd>
<dt><code>&quot;column&quot;</code></dt>
<dd><p>Values are arranged in a single column.
</p>
</dd>
<dt><code>&quot;decreasing&quot;</code></dt>
<dd><p>No value is <var>NaN</var>, and each is less than the preceding one.
</p>
</dd>
<dt><code>&quot;even&quot;</code></dt>
<dd><p>All values are even numbers.
</p>
</dd>
<dt><code>&quot;finite&quot;</code></dt>
<dd><p>All values are finite.
</p>
</dd>
<dt><code>&quot;increasing&quot;</code></dt>
<dd><p>No value is <var>NaN</var>, and each is greater than the preceding one.
</p>
</dd>
<dt><code>&quot;integer&quot;</code></dt>
<dd><p>All values are integer.  This is different than using <code>isinteger</code>
which only checks its an integer type.  This checks that each value in
<var>A</var> is an integer value, i.e., it has no decimal part.
</p>
</dd>
<dt><code>&quot;ncols&quot;</code></dt>
<dd><p>Has exactly as many columns as the next value in <var>attributes</var>.
</p>
</dd>
<dt><code>&quot;ndims&quot;</code></dt>
<dd><p>Has exactly as many dimensions as the next value in <var>attributes</var>.
</p>
</dd>
<dt><code>&quot;nondecreasing&quot;</code></dt>
<dd><p>No value is <var>NaN</var>, and each is greater than or equal to the preceding
one.
</p>
</dd>
<dt><code>&quot;nonempty&quot;</code></dt>
<dd><p>It is not empty.
</p>
</dd>
<dt><code>&quot;nonincreasing&quot;</code></dt>
<dd><p>No value is <var>NaN</var>, and each is less than or equal to the preceding one.
</p>
</dd>
<dt><code>&quot;nonnan&quot;</code></dt>
<dd><p>No value is a <code>NaN</code>.
</p>
</dd>
<dt><code>&quot;nonnegative&quot;</code></dt>
<dd><p>All values are non negative.
</p>
</dd>
<dt><code>&quot;nonsparse&quot;</code></dt>
<dd><p>It is not a sparse matrix.
</p>
</dd>
<dt><code>&quot;nonzero&quot;</code></dt>
<dd><p>No value is zero.
</p>
</dd>
<dt><code>&quot;nrows&quot;</code></dt>
<dd><p>Has exactly as many rows as the next value in <var>attributes</var>.
</p>
</dd>
<dt><code>&quot;numel&quot;</code></dt>
<dd><p>Has exactly as many elements as the next value in <var>attributes</var>.
</p>
</dd>
<dt><code>&quot;odd&quot;</code></dt>
<dd><p>All values are odd numbers.
</p>
</dd>
<dt><code>&quot;positive&quot;</code></dt>
<dd><p>All values are positive.
</p>
</dd>
<dt><code>&quot;real&quot;</code></dt>
<dd><p>It is a non-complex matrix.
</p>
</dd>
<dt><code>&quot;row&quot;</code></dt>
<dd><p>Values are arranged in a single row.
</p>
</dd>
<dt><code>&quot;scalar&quot;</code></dt>
<dd><p>It is a scalar.
</p>
</dd>
<dt><code>&quot;size&quot;</code></dt>
<dd><p>Its size has length equal to the values of the next in <var>attributes</var>.
The next value must is an array with the length for each dimension.  To
ignore the check for a certain dimension, the value of <code>NaN</code> can be
used.
</p>
</dd>
<dt><code>&quot;square&quot;</code></dt>
<dd><p>Is a square matrix.
</p>
</dd>
<dt><code>&quot;vector&quot;</code></dt>
<dd><p>Values are arranged in a single vector (column or vector).
</p>
</dd>
</dl>


<p><strong>See also:</strong> <a href="Built_002din-Data-Types.html#XREFisa">isa</a>, <a href="#XREFvalidatestring">validatestring</a>, <a href="#XREFinputParser">inputParser</a>.
</p></dd></dl>


<p>If none of the preceding functions is sufficient there is also the class
<code>inputParser</code> which can perform extremely complex input checking for
functions.
</p>
<a name="XREFinputParser"></a><dl>
<dt><a name="index-inputParser"></a>Function File: <em><var>p</var> =</em> <strong>inputParser</strong> <em>()</em></dt>
<dd><p>Create object <var>p</var> of the inputParser class.
</p>
<p>This class is designed to allow easy parsing of function arguments.  The
class supports four types of arguments:
</p>
<ol>
<li> mandatory (see <code>addRequired</code>);

</li><li> optional (see <code>addOptional</code>);

</li><li> named (see <code>addParamValue</code>);

</li><li> switch (see <code>addSwitch</code>).
</li></ol>

<p>After defining the function API with these methods, the supplied arguments
can be parsed with the <code>parse</code> method and the parsing results
accessed with the <code>Results</code> accessor.
</p>
</dd></dl>
<dl>
<dt><a name="index-inputParser_002eParameters"></a>Accessor method: <em></em> <strong>inputParser.Parameters</strong></dt>
<dd><p>Return list of parameter names already defined.
</p>
</dd></dl>
<dl>
<dt><a name="index-inputParser_002eResults"></a>Accessor method: <em></em> <strong>inputParser.Results</strong></dt>
<dd><p>Return structure with argument names as fieldnames and corresponding values.
</p>
</dd></dl>
<dl>
<dt><a name="index-inputParser_002eUnmatched"></a>Accessor method: <em></em> <strong>inputParser.Unmatched</strong></dt>
<dd><p>Return structure similar to <code>Results</code>, but for unmatched parameters.
See the <code>KeepUnmatched</code> property.
</p>
</dd></dl>
<dl>
<dt><a name="index-inputParser_002eUsingDefaults"></a>Accessor method: <em></em> <strong>inputParser.UsingDefaults</strong></dt>
<dd><p>Return cell array with the names of arguments that are using default values.
</p>
</dd></dl>
<dl>
<dt><a name="index-inputParser_002eCaseSensitive"></a>Class property: <em></em> <strong>inputParser.CaseSensitive</strong> <em>= <var>boolean</var></em></dt>
<dd><p>Set whether matching of argument names should be case sensitive.  Defaults
to false.
</p>
</dd></dl>
<dl>
<dt><a name="index-inputParser_002eFunctionName"></a>Class property: <em></em> <strong>inputParser.FunctionName</strong> <em>= <var>name</var></em></dt>
<dd><p>Set function name to be used in error messages; Defaults to empty string.
</p>
</dd></dl>
<dl>
<dt><a name="index-inputParser_002eKeepUnmatched"></a>Class property: <em></em> <strong>inputParser.KeepUnmatched</strong> <em>= <var>boolean</var></em></dt>
<dd><p>Set whether an error should be given for non-defined arguments.  Defaults to
false.  If set to true, the extra arguments can be accessed through
<code>Unmatched</code> after the <code>parse</code> method.  Note that since
<code>Switch</code> and <code>ParamValue</code> arguments can be mixed, it is
not possible to know the unmatched type.  If argument is found unmatched
it is assumed to be of the <code>ParamValue</code> type and it is expected to
be followed by a value.
</p>
</dd></dl>
<dl>
<dt><a name="index-inputParser_002eStructExpand"></a>Class property: <em></em> <strong>inputParser.StructExpand</strong> <em>= <var>boolean</var></em></dt>
<dd><p>Set whether a structure can be passed to the function instead of
parameter/value pairs.  Defaults to true.  Not implemented yet.
</p>
<p>The following example shows how to use this class:
</p>
<div class="example">
<pre class="example">function check (varargin)
  p = inputParser ();                      # create object
  p.FunctionName = &quot;check&quot;;                # set function name
  p.addRequired (&quot;pack&quot;, @ischar);         # mandatory argument
  p.addOptional (&quot;path&quot;, pwd(), @ischar);  # optional argument

  ## create a function handle to anonymous functions for validators
  val_mat = @(x) isvector (x) &amp;&amp; all (x &lt;= 1) &amp;&amp; all (x &gt;= 0);
  p.addOptional (&quot;mat&quot;, [0 0], val_mat);

  ## create two arguments of type &quot;ParamValue&quot;
  val_type = @(x) any (strcmp (x, {&quot;linear&quot;, &quot;quadratic&quot;}));
  p.addParamValue (&quot;type&quot;, &quot;linear&quot;, val_type);
  val_verb = @(x) any (strcmp (x, {&quot;low&quot;, &quot;medium&quot;, &quot;high&quot;}));
  p.addParamValue (&quot;tolerance&quot;, &quot;low&quot;, val_verb);

  ## create a switch type of argument
  p.addSwitch (&quot;verbose&quot;);

  p.parse (varargin{:});  # Run created parser on inputs

  ## the rest of the function can access inputs by using p.Results.
  ## for example, get the tolerance input with p.Results.tolerance
endfunction
</pre><pre class="example">

check (&quot;mech&quot;);           # valid, use defaults for other arguments
check ();                 # error, one argument is mandatory
check (1);                # error, since ! ischar
check (&quot;mech&quot;, &quot;~/dev&quot;);  # valid, use defaults for other arguments

check (&quot;mech&quot;, &quot;~/dev&quot;, [0 1 0 0], &quot;type&quot;, &quot;linear&quot;);  # valid

## following is also valid.  Note how the Switch argument type can
## be mixed into or before the ParamValue argument type (but it
## must still appear after any Optional argument).
check (&quot;mech&quot;, &quot;~/dev&quot;, [0 1 0 0], &quot;verbose&quot;, &quot;tolerance&quot;, &quot;high&quot;);

## following returns an error since not all optional arguments,
## `path' and `mat', were given before the named argument `type'.
check (&quot;mech&quot;, &quot;~/dev&quot;, &quot;type&quot;, &quot;linear&quot;);
</pre></div>

<p><em>Note 1</em>: A function can have any mixture of the four API types but
they must appear in a specific order.  <code>Required</code> arguments must be
first and can be followed by any <code>Optional</code> arguments.  Only
the <code>ParamValue</code> and <code>Switch</code> arguments may be mixed
together and they must appear at the end.
</p>
<p><em>Note 2</em>: If both <code>Optional</code> and <code>ParamValue</code> arguments
are mixed in a function API then once a string Optional argument fails to
validate it will be considered the end of the <code>Optional</code>
arguments.  The remaining arguments will be compared against any
<code>ParamValue</code> or <code>Switch</code> arguments.
</p>

<p><strong>See also:</strong> <a href="Defining-Functions.html#XREFnargin">nargin</a>, <a href="#XREFvalidateattributes">validateattributes</a>, <a href="#XREFvalidatestring">validatestring</a>, <a href="#XREFvarargin">varargin</a>.
</p></dd></dl>


<a name="XREFvarargin"></a><a name="XREFvarargout"></a><hr>
<div class="header">
<p>
Next: <a href="Variable_002dlength-Argument-Lists.html#Variable_002dlength-Argument-Lists" accesskey="n" rel="next">Variable-length Argument Lists</a>, Previous: <a href="Defining-Functions.html#Defining-Functions" accesskey="p" rel="prev">Defining Functions</a>, Up: <a href="Functions-and-Scripts.html#Functions-and-Scripts" accesskey="u" rel="up">Functions and Scripts</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
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