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<span class="path"><a href="index.html">FOSSEE Signal Processing Toolbox</a> >> <a href="section_cc2bc01c47967d47fcf3507a91d572ba.html">FOSSEE Signal Processing Toolbox</a> > invfreq</span>
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<div class="refnamediv"><h1 class="refname">invfreq</h1>
<p class="refpurpose">Calculates inverse frequency vectors</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="functionid">invfreq</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">[</span><span class="default">B</span><span class="default">,</span><span class="default">A</span><span class="default">] = </span><span class="functionid">invfreq</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="functionid">invfreq</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">plane</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="functionid">invfreq</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">plane</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,It is assumed that A and B are real polynomials, hence H is one-sided.</p></dd></dt>
<dt><span class="term">F:</span>
<dd><p class="para">vector of frequency samples in radians</p></dd></dt>
<dt><span class="term">nA:</span>
<dd><p class="para">order of denominator polynomial A</p></dd></dt>
<dt><span class="term">nB:</span>
<dd><p class="para">order of numerator polynomial B</p></dd></dt></dl></div>
<div class="refsection"><h3 class="title">Description</h3>
<p class="para">Fit filter B(z)/A(z) or B(s)/A(s) to complex frequency response at frequency points F. A and B are real polynomial coefficients of order nA and nB respectively. Optionally, the fit-errors can be weighted vs frequency according to the weights W. Also, the transform plane can be specified as either 's' for continuous time or 'z' for discrete time. 'z' is chosen by default. Eventually, Steiglitz-McBride iterations will be specified by iter and tol.</p>
<p class="para"></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">12</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">w</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="scilabdefault">,</span><span class="scilabnumber">128</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="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="scilabdefault">;</span>
<span class="scilabid">Hh</span> <span class="scilaboperator">=</span> <span class="scilabid">freqz</span><span class="scilabopenclose">(</span><span class="scilabid">Bh</span><span class="scilabdefault">,</span><span class="scilabid">Ah</span><span class="scilabopenclose">)</span><span class="scilabdefault">;</span>
<a class="scilabcommand" href="scilab://disp">disp</a><span class="scilabopenclose">(</span><a class="scilabcommand" href="scilab://sprintf">sprintf</a><span class="scilabopenclose">(</span><span class="scilabstring">'</span><span class="scilabstring">||frequency response error|| = %f</span><span class="scilabstring">'</span><span class="scilabdefault">,</span><a class="scilabcommand" href="scilab://norm">norm</a><span class="scilabopenclose">(</span><span class="scilabid">H</span><span class="scilaboperator">-</span><span class="scilabid">Hh</span><span class="scilabopenclose">)</span><span class="scilabopenclose">)</span><span class="scilabopenclose">)</span><span class="scilabdefault">;</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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