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<span class="path"><a href="index.html">FOSSEE Signal Processing Toolbox</a> >> <a href="section_e54aa8aac34aa55341e8b4b782fe1a74.html">FOSSEE Signal Processing Toolbox</a> > invfreqz</span>
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<div class="refnamediv"><h1 class="refname">invfreqz</h1>
<p class="refpurpose">Fit filter B(z)/A(z)to the complex frequency response H at frequency points F. A and B are real polynomial coefficients of order nA and nB.</p></div>
<div class="refsynopsisdiv"><h3 class="title">Calling Sequence</h3>
<div class="synopsis"><pre><span class="default">[</span><span class="default">B</span><span class="default">,</span><span class="default">A</span><span class="default">,</span><span class="default">C</span><span class="default">] = </span><span class="functionid">invfreqz</span><span class="default">(</span><span class="default">H</span><span class="default">,</span><span class="default">F</span><span class="default">,</span><span class="default">nB</span><span class="default">,</span><span class="default">nA</span><span class="default">,</span><span class="default">W</span><span class="default">,</span><span class="default">iter</span><span class="default">,</span><span class="default">tol</span><span class="default">,</span><span class="default">trace</span><span class="default">)</span>
<span class="default">[</span><span class="default">B</span><span class="default">,</span><span class="default">A</span><span class="default">,</span><span class="default">C</span><span class="default">] = </span><span class="functionid">invfreqz</span><span class="default">(</span><span class="default">H</span><span class="default">,</span><span class="default">F</span><span class="default">,</span><span class="default">nB</span><span class="default">,</span><span class="default">nA</span><span class="default">,</span><span class="default">W</span><span class="default">)</span>
<span class="default">[</span><span class="default">B</span><span class="default">,</span><span class="default">A</span><span class="default">,</span><span class="default">C</span><span class="default">] = </span><span class="functionid">invfreqz</span><span class="default">(</span><span class="default">H</span><span class="default">,</span><span class="default">F</span><span class="default">,</span><span class="default">nB</span><span class="default">,</span><span class="default">nA</span><span class="default">)</span></pre></div></div>
<div class="refsection"><h3 class="title">Parameters</h3>
<dl><dt><span class="term">H:</span>
<dd><p class="para">desired complex frequency response.</p></dd></dt>
<dt><span class="term">F:</span>
<dd><p class="para">frequency (must be same length as H).</p></dd></dt>
<dt><span class="term">nB:</span>
<dd><p class="para">order of the numerator polynomial B.</p></dd></dt>
<dt><span class="term">nA:</span>
<dd><p class="para">order of the denominator polynomial A.</p></dd></dt>
<dt><span class="term">W:</span>
<dd><p class="para">vector of weights (must be same length as F).</p></dd></dt></dl></div>
<div class="refsection"><h3 class="title">Description</h3>
<p class="para">This is an Octave function.
Fit filter B(z)/A(z)to the complex frequency response H at frequency points F. A and B are real polynomial coefficients of order nA and nB.
Optionally, the fit-errors can be weighted vs frequency according to the weights W.
Note: all the guts are in invfreq.m</p></div>
<div class="refsection"><h3 class="title">Examples</h3>
<div class="programlisting"><table border="0" width="100%"><tr><td width="98%"><pre class="scilabcode"><span class="scilabopenclose">[</span><span class="scilabid">B</span><span class="scilabdefault">,</span><span class="scilabid">A</span><span class="scilabopenclose">]</span> <span class="scilaboperator">=</span> <span class="scilabid">butter</span><span class="scilabopenclose">(</span><span class="scilabnumber">4</span><span class="scilabdefault">,</span><span class="scilabnumber">1</span><span class="scilaboperator">/</span><span class="scilabnumber">4</span><span class="scilabopenclose">)</span><span class="scilabdefault">;</span>
<span class="scilabopenclose">[</span><span class="scilabid">H</span><span class="scilabdefault">,</span><span class="scilabid">F</span><span class="scilabopenclose">]</span> <span class="scilaboperator">=</span> <span class="scilabid">freqz</span><span class="scilabopenclose">(</span><span class="scilabid">B</span><span class="scilabdefault">,</span><span class="scilabid">A</span><span class="scilabopenclose">)</span><span class="scilabdefault">;</span>
<span class="scilabopenclose">[</span><span class="scilabid">Bh</span><span class="scilabdefault">,</span><span class="scilabid">Ah</span><span class="scilabdefault">,</span><span class="scilabid">C</span><span class="scilabopenclose">]</span> <span class="scilaboperator">=</span> <span class="scilabid">invfreq</span><span class="scilabopenclose">(</span><span class="scilabid">H</span><span class="scilabdefault">,</span><span class="scilabid">F</span><span class="scilabdefault">,</span><span class="scilabnumber">4</span><span class="scilabdefault">,</span><span class="scilabnumber">4</span><span class="scilabopenclose">)</span>
<span class="scilabid">Bh</span> <span class="scilaboperator">=</span>
<span class="scilabnumber">0.010209</span> <span class="scilabnumber">0.040838</span> <span class="scilabnumber">0.061257</span> <span class="scilabnumber">0.040838</span> <span class="scilabnumber">0.010209</span>
<span class="scilabid">Ah</span> <span class="scilaboperator">=</span>
<span class="scilabnumber">1.00000</span> <span class="scilaboperator">-</span><span class="scilabnumber">1.96843</span> <span class="scilabnumber">1.73586</span> <span class="scilaboperator">-</span><span class="scilabnumber">0.72447</span> <span class="scilabnumber">0.12039</span>
<span class="scilabid">C</span> <span class="scilaboperator">=</span> <span class="scilaboperator">-</span><span class="scilabnumber">7.7065e-15</span></pre></td><td valign="top"><a href="scilab://scilab.execexample/"><img src="ScilabExecute.png" border="0"/></a></td><td valign="top"><a href="scilab://scilab.editexample/"><img src="ScilabEdit.png" border="0"/></a></td><td></td></tr></table></div></div>
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