
<A NAME=VECTOR>

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



<B>VECTOR</B> _ _ _  _ _ _  _ _ _  _ _ _ <B>declaration</B><P>
<P>
 
The <em>vector</em> declaration declares that its arguments are of type <em>vect
or</em>. 
 <P> <H3> 
syntax: </H3>
<P>
<P>
<em>vector</em>&lt;identifier&gt;{,&lt;identifier&gt;}* 
<P>
<P>
<P>
&lt;identifier&gt; must be a valid REDUCE identifier. It may have already been 
used for a matrix, array, operator or scalar variable. After an identifier 
has been declared to be a vector, it may not be used as a scalar variable. 
<P>
<P>
Vectors are special entities for high-energy physics calculations. You 
cannot put values into their coordinates; they do not have coordinates. 
They are legal arguments for the high-energy physics operators 

<A HREF=r37_0410.html>eps</A>, 
<A HREF=r37_0411.html>g</A> and <em>.</em> (dot). Vector variables are 
used to represent gamma matrices and gamma matrices contracted with Lorentz 
4-vectors, since there are no Dirac variables per se in the system. 
Vectors do follow the usual vector rules for arithmetic operations: 
<em>+</em> and <em>-</em> operate upon two or more vectors, producing a 
vector; <em>*</em> and <em>/</em> cannot be used between vectors; the 
scalar product is represented by the . operator; and the product of a 
scalar and vector expression is well defined, and is a vector. 
<P>
<P>
You can represent components of vectors by including representations of unit 
vectors in your system. For instance, letting <em>E0</em> represent the unit 
vector (1,0,0,0), the command 
<P>
<P>
<em>V1.E0 := 0;</em>would set up the substitution of zero for the first componen
t of the vector 
<em>V1</em>. 
<P>
<P>
Identifiers that are declared by the <em>index</em> and <em>mass</em> declaratio
ns are 
automatically declared to be vectors. 
<P>
<P>
The following errors can occur in calculations using the high energy 
physics package: 
<P>
<P>
<em>A represents only gamma5 in vector expressions</em>You have tried to use A i
n some way other than gamma5 in a 
high-energy physics expression. 
<P>
<P>
<P>
<em>Gamma5 not allowed unless vecdim is 4</em>You have used gamma_5 in a high-en
ergy physics 
computation involving a vector dimension other than 4. 
<P>
<P>
<P>
&lt;ID&gt; <em>has no mass</em> 
<P>
<P>
One of the arguments to 
<A HREF=r37_0414.html>mshell</A> has had no mass assigned to it, in 
high-energy physics calculations. 
<P>
<P>
<P>
<em>Missing arguments for G operator</em>A line symbol is missing in a gamma mat
rix expression in high-energy physics 
calculations. 
<P>
<P>
<P>
<em>Unmatched index</em>&lt;list&gt; 
<P>
<P>
The parser has found unmatched indices during the evaluation of a 
gamma matrix expression in high-energy physics calculations. 
<P>
<P>
<P>
<P>
<P>
