<A NAME=HE_dot>
<TITLE>HE_dot</TITLE></A>
<b><a href=r37_idx.html>INDEX</a></b><p><p>
<B>.</B> _ _ _ <B>HE-DOT</B> _ _ _ _ _ _ _ _ _ _ _ _ <B>operator</B><P>
<P>
The . operator is used to denote the scalar product of two Lorentz
four-vectors.
<P> <H3>
syntax: </H3>
<P>
<P>
<vector> <em>.</em> <vector>
<P>
<P>
<P>
<vector> must be an identifier declared to be of type <em>vector</em> to h
ave
the scalar product definition. When applied to arguments that are not
vectors, the
<A HREF=r37_0043.html>cons</A> operator is used,
whose symbol is also ``dot.''
<P>
<P>
<P> <H3>
examples: </H3>
<P><PRE><TT>
vector aa,bb,cc;
let aa.bb = 0;
aa.bb;
0
aa.cc;
AA.CC
q := aa.cc;
Q := AA.CC
q;
AA.CC
</TT></PRE><P>Since vectors are special high-energy physics entities that do not
contain
values, the . product will not return a true scalar product. You can
assign a scalar identifier to the result of a . operation, or assign a .
operation to have the value of the scalar you supply, as shown above. Note
that the result of a . operation is a scalar, not a vector.
<P>
<P>
The metric tensor g(u,v) can be represented by <em>u.v</em>. If contraction
over the indices is required, <em>u</em> and <em>v</em> should be declared to
be of type
<A HREF=r37_0412.html>index</A>.
<P>
<P>
The dot operator has the highest precedence of the infix operators, so
expressions involving . and other operators have the scalar product
evaluated first before other operations are done.
<P>
<P>
<P>