ame="Brief_I/O">Brief_I/O</a></h4>
<PRE>
 
   The function returns half the value of pi. 
 </PRE>
<h4><a name="Detailed_Input">Detailed_Input</a></h4>
<PRE>
 
   None. 
 </PRE>
<h4><a name="Detailed_Output">Detailed_Output</a></h4>
<PRE>
 
   The function returns half the value of pi (the ratio of 
   a circle's circumference to its diameter), determined by 
   the ACOS function. That is, 
 
         <b>halfpi_c</b> = acos ( -1.0 ) * 0.50 
 </PRE>
<h4><a name="Parameters">Parameters</a></h4>
<PRE>
 
   None