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author Daniele Nicolodi <nicolodi@science.unitn.it>
date Wed, 23 Nov 2011 19:22:13 +0100
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11 <title>Select and find data from an AO (LTPDA Toolbox)</title>
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26 <td valign="baseline"><b>LTPDA Toolbox</b></td><td><a href="../helptoc.html">contents</a></td>
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29 "ltpda_training_topic_2_6.html"><img src="b_prev.gif" border="0" align=
30 "bottom" alt="Whitening noise"></a>&nbsp;&nbsp;&nbsp;<a href=
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32 "bottom" alt="Split and join AOs"></a></td>
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35
36 <h1 class="title"><a name="f3-12899" id="f3-12899"></a>Select and find data from an AO</h1>
37 <hr>
38
39 <p>
40
41 <p>
42 LTPDA contains a set of methods that can be used for the selection of data from an AO. In this section
43 we will in particular look at <tt>ao/find</tt> and <tt>ao/select</tt>.
44 </p>
45 <p>
46 We will start by generating a sine wave:
47 </p>
48 <div class="fragment"><pre>
49 pl = plist(<span class="string">'waveform'</span>, <span class="string">'sine wave'</span>, <span class="string">'f'</span>, 1, <span class="string">'fs'</span>, 100, <span class="string">'nsecs'</span>, 10, <span class="string">'yunits'</span>, <span class="string">'V'</span>);
50 a = ao(pl)
51 </pre></div>
52
53 <br>
54 <h2>Example 1 - using <tt>find</tt></h2>
55 <p>
56 Now let us use the <tt>find</tt> method to extract parts of the data we are interested in.
57 </p>
58 <p>
59 The <tt>find</tt> method can take a parameter 'query' for defining which data points you want to find. The
60 query string can be any valid MATLAB logical expression, and in particular can be expressed in terms of the
61 x and y data of the input AO.
62 </p>
63 <p>
64 In this example, we want to find all x values between 3 and 6. The following code does just that:
65 </p>
66 <div class="fragment"><pre>
67 a_find = find(a, plist(<span class="string">'query'</span>, <span class="string">'x&gt;3 &amp; x&lt;6'</span>));
68 iplot(a, a_find)
69 </pre></div>
70 <img src="images/ltpda_training_1/topic2/find.png" alt="find" border="1">
71 <br>
72 <h2>Example 2 - using <tt>select</tt></h2>
73 <p>
74 The <tt>select</tt> method lets us select a set of data samples from our AO.
75 For this we need a <tt>plist</tt> containing an array of samples we want to select.
76 We take our sine wave again which is stored in the variable <tt>a</tt> to see how it works.
77 </p>
78 <div class="fragment"><pre>
79 a_select = select(a, plist(<span class="string">'samples'</span>, 200:800));
80 iplot(a, a_select)
81 </pre></div>
82 <img src="images/ltpda_training_1/topic2/select.png" alt="select" border="1">
83
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95 <td align="left">Whitening noise</td>
96
97 <td>&nbsp;</td>
98
99 <td align="right">Split and join AOs</td>
100
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