code changes by Sonu Sharma during FOSSEE Fellowship 2018

1 files changed, 28 insertions, 24 deletions

diff --git a/help/en_US/butter.xml b/help/en_US/butter.xml
index bacacaf..8137c23 100644
--- a/help/en_US/butter.xml
+++ b/help/en_US/butter.xml
@@ -17,20 +17,19 @@
 
   <refnamediv>
     <refname>butter</refname>
-    <refpurpose>This function generates a Butterworth filter.</refpurpose>
+    <refpurpose>Butterworth filter design..</refpurpose>
   </refnamediv>
 
 
 <refsynopsisdiv>
    <title>Calling Sequence</title>
    <synopsis>
-   [a, b] = butter (n, w)
-   [a, b] = butter (n, w, "high")
-   [a, b] = butter (n, [wl, wh])
-   [b, a] = butter (n, [wl, wh], "stop")
-   [a, b, c] = butter (…)
-   [a, b, c, d] = butter (…)
-   […] = butter (…, "s")
+    [b, a] = butter (n, wc)
+    [b, a] = butter (n, wc, "high")
+    [b, a] = butter (n, [wl, wh])
+    [b, a] = butter (n, [wl, wh], "stop")
+    [z, p, g] = butter (…)
+    […] = butter (…, "s")
    </synopsis>
 </refsynopsisdiv>
 
@@ -38,34 +37,39 @@
    <title>Parameters</title>
    <variablelist>
    <varlistentry><term>n:</term>
-      <listitem><para> positive integer value</para></listitem></varlistentry>
-   <varlistentry><term>w:</term>
-      <listitem><para> positive real value, w in the range [0,1]</para></listitem></varlistentry>
+      <listitem><para> positive integer value (order of filter).</para></listitem></varlistentry>
+   <varlistentry><term>wc:</term>
+      <listitem><para> positive real value,</para><para>    1).Normalised digital 3dB cutoff frequency/frequencies for digital filter, in the range [0, 1] {dimensionless}</para><para>    2).Analog 3dB cutoff frequency/frequencies for analog filter, in the range [0, Inf] {rad/sec}</para></listitem></varlistentry>
    </variablelist>
 </refsection>
 
 <refsection>
    <title>Description</title>
    <para>
-This is an Octave function.
-This function generates a Butterworth filter. Default is a discrete space (Z) filter.
-The third parameter takes in low or high, default value is low. The cutoff is pi*Wc radians.
-[b,a] = butter(n, [Wl, Wh]) indicates a band pass filter with edges pi*Wl and pi*Wh radians.
-[b,a] = butter(n, [Wl, Wh], ’stop’) indicates a band reject filter with edges pi*Wl and pi*Wh radians.
-[z,p,g] = butter(...) returns filter as zero-pole-gain rather than coefficients of the numerator and denominator polynomials.
-[...] = butter(...,’s’) returns a Laplace space filter, w can be larger than 1.
-[a,b,c,d] = butter(...) returns state-space matrices.
+This function generates a Butterworth filter. Default is a discrete space (z) or digital filter using Bilinear transformation from s to z plane.</para>
+ <para>If second argument is scalar the third parameter takes in low or high, default value is low. The cutoff is pi*wc radians.</para>
+ <para>[b,a] = butter(n, [wl, wh]) indicates a band pass filter with cutoffs pi*Wl and pi*wh radians. </para>
+ <para>[b,a] = butter(n, [wl, wh], ’stop’) indicates a band reject filter with cutoffs pi*wl and pi*wh radians.</para>
+ <para>[z,p,g] = butter(...) returns filter as zero-pole-gain rather than coefficients of the numerator and denominator polynomials.</para>
+ <para>[...] = butter(...,’s’) returns a Laplace space filter,here cutoff(s) wc can be larger than 1 (rad/sec).
 </para>
 </refsection>
 
 <refsection>
    <title>Examples</title>
    <programlisting role="example"><![CDATA[
-[a,b]=butter(3, 0.7)
-a =
-0.37445   1.12336   1.12336   0.37445
-b =
-1.00000   1.16192   0.69594   0.13776
+n = 4;
+wc = 0.3;
+[b a] = butter(n, wc, "high")
+
    ]]></programlisting>
 </refsection>
+
+<refsection>
+<title>Modified by :</title>
+<simplelist type="vert">
+<member>Sonu Sharma, RGIT Mumbai (fellow at FOSSEE, IIT Bombay)</member>
+    </simplelist>
+</refsection>
+
 </refentry>