Create a lookup table allowing sites in this lattice to be queried using `self.site_lookup[n]` where `n` is the identifying site numbe.

        Args:
            None

        Returns:
            None

def initialise_site_lookup_table( self ):
        """
        Create a lookup table allowing sites in this lattice to be queried using `self.site_lookup[n]` where `n` is the identifying site numbe.

        Args:
            None

        Returns:
            None
        """
        self.site_lookup = {}
        for site in self.sites:
            self.site_lookup[ site.number ] = site