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<H3 CLASS="subsection"><A NAME="htoc336">8.9</A>  Labeling constraints</H3><UL>
<LI><A HREF="gprolog063.html#toc275"><TT>fd_labeling/2</TT>,
<TT>fd_labeling/1</TT>,
<TT>fd_labelingff/1</TT></A>
</LI></UL>
<H4 CLASS="subsubsection"><A NAME="toc275"></A><A NAME="htoc337">8.9.1</A>  <TT>fd_labeling/2</TT>,
<TT>fd_labeling/1</TT>,
<TT>fd_labelingff/1</TT></H4><P>
<A NAME="fd-labeling/2"></A>
</P><P><B>Templates</B></P><DL CLASS="list"><DT CLASS="dt-list">
</DT><DD CLASS="dd-list"><TT>
fd_labeling(+fd_variable_list, +fd_labeling_option_list)<BR>
fd_labeling(+fd_variable, +fd_labeling_option_list)<BR>
fd_labeling(+fd_variable_list)<BR>
fd_labeling(+fd_variable)<BR>
fd_labelingff(+fd_variable_list)<BR>
fd_labelingff(+fd_variable)</TT></DD></DL><P><B>Description</B></P><P><TT>fd_labeling(Vars, Options)</TT> assigns a value to each variable
<TT>X</TT> of the list <TT>Vars</TT> according to the list of labeling
options given by <TT>Options</TT>. <TT>Vars</TT> can be also a single FD
variable. This predicate is re-executable on backtracking.</P><P><B>FD labeling options</B>: <TT>Options</TT> is a list of labeling
options. If this list contains contradictory options, the rightmost option
is the one which applies. Possible options are:</P><UL CLASS="itemize"><LI CLASS="li-itemize"><TT>variable_method(V)</TT>: specifies the
heuristics to select the variable to enumerate:<UL CLASS="itemize"><LI CLASS="li-itemize"><TT>standard</TT>: no heuristics, the leftmost variable is selected.</LI><LI CLASS="li-itemize"><TT>first_fail</TT> (or <TT>ff</TT>): selects the variable with the
smallest number of elements in its domain. If several variables have the
same number of elements the leftmost variable is selected.</LI><LI CLASS="li-itemize"><TT>most_constrained</TT>: like <TT>first_fail</TT> but when
several variables have the same number of elements selects the
variable that appears in most constraints.</LI><LI CLASS="li-itemize"><TT>smallest</TT>: selects the variable that has the smallest value
in its domain. If there is more than one such variable selects the
variable that appears in most constraints.</LI><LI CLASS="li-itemize"><TT>largest</TT>: selects the variable that has the greatest value in
its domain. If there is more than one such variable selects the variable
that appears in most constraints.</LI><LI CLASS="li-itemize"><TT>max_regret</TT>: selects the variable that has the greatest
difference between the smallest value and the next value of its domain. If
there is more than one such variable selects the variable that appears in
most constraints.</LI><LI CLASS="li-itemize"><TT>random</TT>: selects randomly a variable. Each variable is only
chosen once.</LI></UL><P>The default value is <TT>standard</TT>.</P></LI><LI CLASS="li-itemize"><TT>reorder(true/false)</TT>: specifies if the variable
heuristics should dynamically reorder the list of variable (<TT>true</TT>) or
not (<TT>false</TT>). Dynamic reordering is generally more efficient but in
some cases a static ordering is faster. The default value is
<TT>true</TT>.</LI><LI CLASS="li-itemize"><TT>value_method(V)</TT>: specifies the heuristics
to select the value to assign to the chosen variable:<UL CLASS="itemize"><LI CLASS="li-itemize"><TT>min</TT>: enumerates the values from the smallest to the greatest
(default).</LI><LI CLASS="li-itemize"><TT>max</TT>: enumerates the values from the greatest to the smallest.</LI><LI CLASS="li-itemize"><TT>middle</TT>: enumerates the values from the middle to the bounds.</LI><LI CLASS="li-itemize"><TT>bounds</TT>: enumerates the values from the bounds to the middle.</LI><LI CLASS="li-itemize"><TT>random</TT>: enumerates the values randomly. Each value is only
tried once.</LI></UL><P>The default value is <TT>min</TT>.</P></LI><LI CLASS="li-itemize"><TT>backtracks(B)</TT>: unifies <TT>B</TT> with the
number of backtracks during the enumeration.</LI></UL><P><TT>fd_labeling(Vars)</TT> is equivalent to <TT>fd_labeling(Vars,
[])</TT>.</P><P><TT>fd_labelingff(Vars)</TT> is equivalent to <TT>fd_labeling(Vars,
[variable_method(ff)])</TT>.</P><P><B>Errors</B></P><TABLE CELLSPACING=6 CELLPADDING=0><TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
<TR><TD VALIGN=top ALIGN=left>
<TT>Vars</TT> is a partial list or a list with an element
<TT>E</TT> which is a variable</TD><TD VALIGN=top ALIGN=center NOWRAP>  </TD><TD VALIGN=top ALIGN=left><TT>instantiation_error</TT></TD></TR>
<TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
<TR><TD VALIGN=top ALIGN=left>
<TT>Vars</TT> is neither a partial list nor a list</TD><TD VALIGN=top ALIGN=center NOWRAP>  </TD><TD VALIGN=top ALIGN=left><TT>type_error(list, Vars)</TT></TD></TR>
<TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
<TR><TD VALIGN=top ALIGN=left>
an element <TT>E</TT> of the <TT>Vars</TT> list is neither a
variable nor an integer nor an FD variable</TD><TD VALIGN=top ALIGN=center NOWRAP>  </TD><TD VALIGN=top ALIGN=left><TT>type_error(fd_variable, E)</TT></TD></TR>
<TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
<TR><TD VALIGN=top ALIGN=left>
<TT>Options</TT> is a partial list or a list with an element
<TT>E</TT> which is a variable</TD><TD VALIGN=top ALIGN=center NOWRAP>  </TD><TD VALIGN=top ALIGN=left><TT>instantiation_error</TT></TD></TR>
<TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
<TR><TD VALIGN=top ALIGN=left>
<TT>Options</TT> is neither a partial list nor a list</TD><TD VALIGN=top ALIGN=center NOWRAP>  </TD><TD VALIGN=top ALIGN=left><TT>type_error(list, Options)</TT></TD></TR>
<TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
<TR><TD VALIGN=top ALIGN=left>
an element <TT>E</TT> of the <TT>Options</TT> list is neither a
variable nor a labeling option</TD><TD VALIGN=top ALIGN=center NOWRAP>  </TD><TD VALIGN=top ALIGN=left><TT>domain_error(fd_labeling_option, E)</TT></TD></TR>
<TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
</TABLE><P><B>Portability</B></P><P>GNU Prolog predicates.</P>
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