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



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