scilab/modules/signal_processing/help/en_US/filters/cheb2mag.xml

   1 <?xml version="1.0" encoding="UTF-8"?>
   2 <refentry xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:svg="http://www.w3.org/2000/svg" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:db="http://docbook.org/ns/docbook" xmlns:scilab="http://www.scilab.org" xml:lang="en" xml:id="cheb2mag">
   3     <refnamediv>
   4         <refname>cheb2mag</refname>
   5         <refpurpose>response of type 2 Chebyshev filter</refpurpose>
   6     </refnamediv>
   7     <refsynopsisdiv>
   8         <title>Syntax</title>
   9         <synopsis>[h2]=cheb2mag(n,omegar,A,sample)</synopsis>
  10     </refsynopsisdiv>
  11     <refsection>
  12         <title>Arguments</title>
  13         <variablelist>
  14             <varlistentry>
  15                 <term>n</term>
  16                 <listitem>
  17                     <para>integer ; filter order</para>
  18                 </listitem>
  19             </varlistentry>
  20             <varlistentry>
  21                 <term>omegar</term>
  22                 <listitem>
  23                     <para>real scalar : cut-off frequency</para>
  24                 </listitem>
  25             </varlistentry>
  26             <varlistentry>
  27                 <term>A</term>
  28                 <listitem>
  29                     <para>attenuation in stop band</para>
  30                 </listitem>
  31             </varlistentry>
  32             <varlistentry>
  33                 <term>sample</term>
  34                 <listitem>
  35                     <para>vector of frequencies where cheb2mag is evaluated</para>
  36                 </listitem>
  37             </varlistentry>
  38             <varlistentry>
  39                 <term>h2</term>
  40                 <listitem>
  41                     <para>vector of Chebyshev II filter values at sample points</para>
  42                 </listitem>
  43             </varlistentry>
  44         </variablelist>
  45     </refsection>
  46     <refsection>
  47         <title>Description</title>
  48         <para>
  49             Square magnitude response of a type 2 Chebyshev filter.
  50         </para>
  51         <para>
  52             <literal>omegar</literal> = stopband edge, <literal>sample</literal> = vector of
  53             frequencies where the square magnitude <literal>h2</literal> is desired.
  54         </para>
  55     </refsection>
  56     <refsection>
  57         <title>Examples</title>
  58         <programlisting role="example"><![CDATA[
  59 //Chebyshev; ripple in the stopband
  60 n=10;
  61 omegar=6;
  62 A=1/0.2;
  63 Samples=0.0001:0.05:10;
  64 h2=cheb2mag(n,omegar,A,Samples);
  65 plot(Samples,log(h2)/log(10))
  66 xtitle("", "frequencies", "magnitude in dB");
  67
  68 //Plotting of frequency edges
  69 minval=(-max(-log(h2)))/log(10);
  70 plot2d([omegar;omegar],[minval;0],[2],"000");
  71
  72 //Computation of the attenuation in dB at the stopband edge
  73 attenuation=-log(A*A)/log(10);
  74 plot2d(Samples',attenuation*ones(Samples)',[5],"000")
  75  ]]></programlisting>
  76         <scilab:image><![CDATA[
  77 n=10;omegar=6;A=1/0.2;Samples=0.0001:0.05:10;
  78 h2=cheb2mag(n,omegar,A,Samples);
  79 plot(Samples,log(h2)/log(10))
  80 xtitle("", "frequencies", "magnitude in dB");
  81
  82 minval=(-max(-log(h2)))/log(10);
  83 plot2d([omegar;omegar],[minval;0],[2],"000");
  84
  85 attenuation=-log(A*A)/log(10);
  86 plot2d(Samples',attenuation*ones(Samples)',[5],"000")
  87 ]]>     </scilab:image>
  88     </refsection>
  89     <refsection role="see also">
  90         <title>See also</title>
  91         <simplelist type="inline">
  92             <member>
  93                 <link linkend="cheb1mag">cheb1mag</link>
  94             </member>
  95         </simplelist>
  96     </refsection>
  97 </refentry>