File r37/lisp/csl/html/r37_0412.html artifact 8757af3dfd part of check-in 808e24217a

<A NAME=INDEX>

<TITLE>INDEX</TITLE></A>
<b><a href=r37_idx.html>INDEX</a></b><p><p>



<B>INDEX</B> _ _ _  _ _ _  _ _ _  _ _ _ <B>declaration</B><P>
<P>
 
The declaration <em>index</em> flags a four-vector as an index for subsequent 
high-energy physics calculations. 
 <P> <H3> 
syntax: </H3>
<P>
<P>
<em>index</em>&lt;vector-id&gt;{,&lt;vector-id&gt;}* 
<P>
<P>
<P>
&lt;vector-id&gt; must have been declared of type <em>vector</em>. 
<P>
<P>
 <P> <H3> 
examples: </H3>
<P><PRE><TT>
vector aa,bb,cc; 

index uu; 

let aa.bb = 0; 

(aa.uu)*(bb.uu); 

  0 


(aa.uu)*(cc.uu); 

  AA.CC

</TT></PRE><P>Index variables are used to represent contraction over components 
of 
vectors when scalar products are taken by the . operator, as well as 
indicating contraction for the 
<A HREF=r37_0410.html>eps</A> operator or metric tensor. 
<P>
<P>
The special status of a vector as an index can be revoked with the 
declaration 
<A HREF=r37_0416.html>remind</A>. The object remains a vector, however. 
<P>
<P>
<P>