<parameter>k</parameter>-th dimension, <parameter>n</parameter> = 2
        * <parameter>k</parameter> means upper bound of
        <parameter>k</parameter>-th dimension.  Negative
        <parameter>n</parameter> denotes the inverse value of the corresponding
        positive coordinate.  This operator is designed for KNN-GiST support.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <type>cube</type> <literal>&lt;-&gt;</literal> <type>cube</type>
        <returnvalue>float8</returnvalue>
       </para>
       <para>
        Computes the Euclidean distance between the two cubes.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <type>cube</type> <literal>&lt;#&gt;</literal> <type>cube</type>
        <returnvalue>float8</returnvalue>
       </para>
       <para>
        Computes the taxicab (L-1 metric) distance between the two cubes.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <type>cube</type> <literal>&lt;=&gt;</literal> <type>cube</type>
        <returnvalue>float8</returnvalue>
       </para>
       <para>
        Computes the Chebyshev (L-inf metric) distance between the two cubes.
       </para></entry>
      </row>
     </tbody>
   </tgroup>
  </table>

  <para>
   In addition to the above operators, the usual comparison
   operators shown in <xref linkend="functions-comparison-op-table"/> are
   available for type <type>cube</type>.  These
   operators first compare the first coordinates, and if those are equal,
   compare the second coordinates, etc.  They exist mainly to support the
   b-tree index operator class for <type>cube</type>, which can be useful for
   example if you would like a UNIQUE constraint on a <type>cube</type> column.
   Otherwise, this ordering is not of much practical use.
  </para>

  <para>
   The <filename>cube</filename> module also provides a GiST index operator class for
   <type>cube</type> values.
   A <type>cube</type> GiST index can be used to search for values using the
   <literal>=</literal>, <literal>&amp;&amp;</literal>, <literal>@&gt;</literal>, and
   <literal>&lt;@</literal> operators in <literal>WHERE</literal> clauses.
  </para>

  <para>
   In addition, a <type>cube</type> GiST index can be used to find nearest
   neighbors using the metric operators
   <literal>&lt;-&gt;</literal>, <literal>&lt;#&gt;</literal>, and
   <literal>&lt;=&gt;</literal> in <literal>ORDER BY</literal> clauses.
   For example, the nearest neighbor of the 3-D point (0.5, 0.5, 0.5)
   could be found efficiently with:
<programlisting>
SELECT c FROM test ORDER BY c &lt;-&gt; cube(array[0.5,0.5,0.5]) LIMIT 1;
</programlisting>
  </para>

  <para>
   The <literal>~&gt;</literal> operator can also be used in this way to
   efficiently retrieve the first few values sorted by a selected coordinate.
   For example, to get the first few cubes ordered by the first coordinate
   (lower left corner) ascending one could use the following query:
<programlisting>
SELECT c FROM test ORDER BY c ~&gt; 1 LIMIT 5;
</programlisting>
   And to get 2-D cubes ordered by the first coordinate of the upper right
   corner descending:
<programlisting>
SELECT c FROM test ORDER BY c ~&gt; 3 DESC LIMIT 5;
</programlisting>
  </para>

  <para>
   <xref linkend="cube-functions-table"/> shows the available functions.
  </para>

  <table id="cube-functions-table">
   <title>Cube Functions</title>
    <tgroup cols="1">
     <thead>
      <row>
       <entry role="func_table_entry"><para role="func_signature">
        Function
       </para>
       <para>
        Description
       </para>
       <para>
        Example(s)
       </para></entry>
      </row>
     </thead>

     <tbody>
      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <function>cube</function> ( <type>float8</type>