\subsection{Adjacency matrix files}
\label{Adjacency}

Spatial dependencies are defined in an adjacency matrix file. An adjacency matrix file can only be defined to a single one dimension entity (no combines word in its definition). The entity's data file defines the size of the adjacency matrix. The number of rows and columns must be exactly the same in the adjacency matrix as is the number of rows in the entity's data file (excluding comments). Adjacency matrix files must be saved in ASCII format.

Each row (or column) in the adjacency matrix defines the neighbours of a variable. Position (i, j) defines if the i:th and j:th variables are adjacent. Value `0' means that the variables are not adjacent or neighbours and value 1 means they are.

\textbf{Example:}
\begin{verbatim}
A data file:
8 2 3
7 9 2
1 6 7
4 8 9

An adjacency matrix file:
0 1 0 0
1 0 0 0
0 0 0 1
0 0 1 0
\end{verbatim}

Let's assume that variable alpha is defined on the 1st column of the data file. Now actually the alpha group has 4 variables since we have 4 rows in the data file. The variables are $alpha\_1 = 8$, $alpha\_2 = 7$, $alpha\_3 = 1$, and $alpha\_4 = 4$. 

In our example, variable $alpha\_1$'s neighbour is $alpha\_2$ (and $alpha\_2$'s neighbour is $alpha\_1$). $Alpha\_3$'s neighbour is $alpha\_4$.