
<A NAME=EPS>

<TITLE>EPS</TITLE></A>
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<B>EPS</B> _ _ _  _ _ _  _ _ _  _ _ _ <B>operator</B><P>
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The <em>eps</em> operator denotes the completely antisymmetric tensor of 
order 4 and its contraction with Lorentz four-vectors, as used in 
high-energy physics calculations. 
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syntax: </H3>
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<em>eps</em>(&lt;vector-expr&gt;,&lt;vector-expr&gt;,&lt;vector-expr&gt;, 
&lt;vector-expr&gt;) 
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&lt;vector-expr&gt; must be a valid vector expression, and may be an index. 
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examples: </H3>
<P><PRE><TT>
vector g0,g1,g2,g3; 

eps(g1,g0,g2,g3); 

  - EPS(G0,G1,G2,G3); 


eps(g1,g2,g0,g3); 

  EPS(G0,G1,G2,G3); 


eps(g1,g2,g3,g1); 

  0

</TT></PRE><P>Vector identifiers are ordered alphabetically by REDUCE. When an o
dd number 
of transpositions is required to restore the canonical order to the four 
arguments of <em>eps</em>, the term is ordered and carries a minus sign. When an
 
even number of transpositions is required, the term is returned ordered and 
positive. When one of the arguments is repeated, the value 0 is returned. 
A contraction of the form 
eps(_i j mu nu p_mu q_nu) 
is represented by <em>eps(i,j,p,q)</em> when <em>i</em> and <em>j</em> have been
 
declared to be of type 
<A HREF=r37_0412.html>index</A>. 
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