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<h4 class="subsection">15.1.8 Test Plotting Functions</h4>
<p>The functions <code>sombrero</code> and <code>peaks</code> provide a way to check
that plotting is working. Typing either <code>sombrero</code> or <code>peaks</code>
at the Octave prompt should display a three-dimensional plot.
<!-- ./plot/sombrero.m -->
<p><a name="doc_002dsombrero"></a>
<div class="defun">
— Function File: <b>sombrero</b> (<var>n</var>)<var><a name="index-sombrero-1104"></a></var><br>
<blockquote><p>Produce the familiar three-dimensional sombrero plot using <var>n</var>
grid lines. If <var>n</var> is omitted, a value of 41 is assumed.
<p>The function plotted is
<pre class="example"> z = sin (sqrt (x^2 + y^2)) / (sqrt (x^2 + y^2))
</pre>
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<p class="noindent"><strong>See also:</strong> <a href="doc_002dsurf.html#doc_002dsurf">surf</a>, <a href="doc_002dmeshgrid.html#doc_002dmeshgrid">meshgrid</a>, <a href="doc_002dmesh.html#doc_002dmesh">mesh</a>.
</p></blockquote></div>
<!-- ./plot/peaks.m -->
<p><a name="doc_002dpeaks"></a>
<div class="defun">
— Function File: <b>peaks</b> ()<var><a name="index-peaks-1105"></a></var><br>
— Function File: <b>peaks</b> (<var>n</var>)<var><a name="index-peaks-1106"></a></var><br>
— Function File: <b>peaks</b> (<var>x, y</var>)<var><a name="index-peaks-1107"></a></var><br>
— Function File: <var>z</var> = <b>peaks</b> (<var><small class="dots">...</small></var>)<var><a name="index-peaks-1108"></a></var><br>
— Function File: [<var>x</var>, <var>y</var>, <var>z</var>] = <b>peaks</b> (<var><small class="dots">...</small></var>)<var><a name="index-peaks-1109"></a></var><br>
<blockquote><p>Generate a function with lots of local maxima and minima. The function
has the form
<pre class="verbatim"> f(x,y) = 3*(1-x)^2*exp(-x^2 - (y+1)^2) ...
- 10*(x/5 - x^3 - y^5)*exp(-x^2-y^2) ...
- 1/3*exp(-(x+1)^2 - y^2)
</pre>
<p>Called without a return argument, <code>peaks</code> plots the surface of the
above function using <code>mesh</code>. If <var>n</var> is a scalar, the <code>peaks</code>
returns the values of the above function on a <var>n</var>-by-<var>n</var> mesh over
the range <code>[-3,3]</code>. The default value for <var>n</var> is 49.
<p>If <var>n</var> is a vector, then it represents the <var>x</var> and <var>y</var> values
of the grid on which to calculate the above function. The <var>x</var> and
<var>y</var> values can be specified separately.
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<p class="noindent"><strong>See also:</strong> <a href="doc_002dsurf.html#doc_002dsurf">surf</a>, <a href="doc_002dmesh.html#doc_002dmesh">mesh</a>, <a href="doc_002dmeshgrid.html#doc_002dmeshgrid">meshgrid</a>.
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