1 files changed, 69 insertions, 1 deletions
diff --git a/help/en_US/isstable.xml b/help/en_US/isstable.xml
index 295c1d4..9b53add 100644
--- a/help/en_US/isstable.xml
+++ b/help/en_US/isstable.xml
@@ -17,7 +17,75 @@
 
   <refnamediv>
     <refname>isstable</refname>
-    <refpurpose>SOS matrix corresponds to [bi(1) bi(2) bi(3) ai(1) ai(2) ai(3)].</refpurpose>
+    <refpurpose>Checks stability of  given Discrete time system function</refpurpose>
+    <para> </para>
   </refnamediv>
 
+<refsynopsisdiv>
+   <title>Calling Sequence</title>
+   <synopsis>
+flag = ismaxphase(b,a)
+flag = ismaxphase(sos)
+   </synopsis>
+    <para> </para>
+</refsynopsisdiv>
+
+<refsection>
+   <title>Parameters</title>
+   <variablelist>
+   <varlistentry><term>b</term>
+      <listitem><para> Coefficients of numerator polynomial of system function </para></listitem></varlistentry>
+   <varlistentry><term>a</term>
+      <listitem><para> Coefficients of denumerator polynomial of system function</para></listitem></varlistentry>
+   <varlistentry><term>sos</term>
+      <listitem><para> Second order section matrix of order Kx6 </para></listitem></varlistentry>
+   <varlistentry><term>flag</term>
+      <listitem><para> This function returns logical 1 if system is Stable (flag = 1) </para> <para> Otherwise it returns logical 0 (flag = 0)</para></listitem></varlistentry>
+   </variablelist>
+    <para> </para>
+</refsection>
+
+<refsection>
+   <title>Description</title>
+   <para> This function determines whether the given system function is Stable system function or not. Stable system means all poles of transfer function will be inside the unit circle in z-plane </para>
+    <para> </para>
+</refsection>
+
+<refsection>
+   <title>Example : 1 <para>Example of stable system function </para> </title>
+   <para>
+    <latex>
+      \begin{eqnarray}
+      H(z) = \frac{1 +2z^{-1} } {1 -0.7z^{-1} + 0.1 z^{-2} }
+      \end{eqnarray}
+    </latex>
+   </para>
+    <para> </para>
+
+   <programlisting role="example"><![CDATA[
+b = [1 2] ; //Numerator polynomial coefficients
+a = [1 -0.7 0.1] ; //Denumerator polynomial coefficients
+flag = isstable(b,a) //This is an example of Stable system, hence it will give output as : flag = 1
+]]></programlisting>
+</refsection>
+
+<refsection>
+<title> Example : 2 <para>Example of unstable system function</para> </title>
+
+   <para>
+    <latex>
+      \begin{eqnarray}
+      H(z) = \frac{1 +2z^{-1} } {1 +5z^{-1} + 6z^{-2} }
+      \end{eqnarray}
+    </latex>
+   </para>
+    <para> </para>
+
+   <programlisting role="example"><![CDATA[
+b = [1 2] ; //Numerator polynomial coefficients
+a = [1 5 6] ; //Denumerator polynomial coefficients
+flag = isstable(b,a) //This is an example of Unstable system, hence it will give output as : flag = 0
+]]></programlisting>
+</refsection>
+
 </refentry>