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Daniele Nicolodi <nicolodi@science.unitn.it> |
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Mon, 05 Dec 2011 16:20:06 +0100 (2011-12-05) |
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<h1 class="title"><a name="f3-12899" id="f3-12899"></a>Interpolating data</h1>
<hr>
<p>
<h2>Description</h2>
<p>
Interpolation of data can be done in the LTPDA Toolbox by means of
<a href="matlab:doc('ao/interp')"><tt>interp</tt></a>.
This function interpolates the values in the input AO(s) at new values specified by the
input parameter list.
</p>
<p>
<a href="matlab:doc('ao/interp')"><tt>Interp</tt></a> overloads <tt>interp1</tt> function of
Matlab Signal Processing Toolbox for AOs.
</p>
<br>
<br>
<h2>Syntax</h2>
</p>
<div class="fragment"><pre>
<br>
b = interpolate(a, pl)
</pre>
</div>
<h2>Parameters</h2>
<p>
The following parameters can be set in the method:
<ul>
<li> <tt>vertices</tt> - specify the new vertices to interpolate on </li>
<li> <tt>method</tt> - four methods are available for interpolating data</li>
<ul>
<li> 'nearest'- nearest neighbor interpolation </li>
<li> 'linear' - linear interpolation </li>
<li> 'spline' - spline interpolation (default option) </li>
<li> 'cubic' - shape-preserving piecewise cubic interpolation </li>
</ul>
</ul>
For details see <tt>interp1</tt> help of Matlab.
</p>
<p>
<h2>Examples</h2>
</p>
<p>
1. Interpolation of a sequence of random data at original sampling rate of 1 Hz
by a factor of 10 with no initial phase.
</p>
<div class="fragment"><pre>
<br>
<span class="comment">% Signal generation</span>
pl = plist(<span class="string">'tsfcn'</span>,<span class="string">'sin(2*pi*1.733*t)'</span>,...
<span class="string">'fs'</span>,1,<span class="string">'nsecs'</span>,10,...
<span class="string">'yunits'</span>,<span class="string">'V'</span>);
x = ao(pl);
<span class="comment">% Interpolate on a new time vector</span>
t = linspace(0, x.data.nsecs - 1/x.data.fs, 2*len(x));
pl_spline = plist(<span class="string">'vertices'</span>,t);
pl_nearest = plist(<span class="string">'vertices'</span>,t,<span class="string">'method'</span>,<span class="string">'nearest'</span>);
x_spline = interp(x,pl_spline);
x_nearest = interp(x,pl_nearest);
iplot([x x_spline x_nearest], plist(<span class="string">'Markers'</span>, {<span class="string">'x'</span>, <span class="string">'o'</span>, <span class="string">'+'</span>}, ...
<span class="string">'LineColors'</span>, {<span class="string">'k'</span>, <span class="string">'r'</span>}));
</pre>
</div>
<br>
<br>
<img src="images/interp.png" alt="Interpolate" border="0">
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