<!DOCTYPE html> <html> <head> <meta http-equiv="Content-Type" content="text/html; charset=US-ASCII"> <meta name="generator" content="hevea 2.05"> <meta name="Author" content="Daniel Diaz"> <meta name="Keywords" content="GNU Prolog, manual, Prolog, compiler, constraints, finite domains"> <link rel="icon" type="image/x-icon" href="/gprolog.ico"><link rel="stylesheet" type="text/css" href="gprolog.css"> <title>Labeling constraints</title> </head> <body TEXT=black BGCOLOR=white> <a href="gprolog062.html"><img src="previous_motif.gif" alt="Previous"></a> <a href="gprolog054.html"><img src="contents_motif.gif" alt="Up"></a> <a href="gprolog064.html"><img src="next_motif.gif" alt="Next"></a> <hr> <h3 class="subsection" id="sec330">9.9  Labeling constraints</h3> <ul> <li><a href="gprolog063.html#fd-labeling%2F2"><span class="c003">fd_labeling/2</span>, <span class="c003">fd_labeling/1</span>, <span class="c003">fd_labelingff/1</span></a> </li></ul> <h4 class="subsubsection" id="fd-labeling/2">9.9.1  <a id="hevea_default992"></a><span class="c003">fd_labeling/2</span>, <a id="hevea_default993"></a><span class="c003">fd_labeling/1</span>, <a id="hevea_default994"></a><span class="c003">fd_labelingff/1</span></h4> <p><span class="c009">Templates</span></p><dl class="list"><dt class="dt-list"> </dt><dd class="dd-list"><span class="c003"> 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)</span></dd></dl><p><span class="c009">Description</span></p><p><span class="c003">fd_labeling(Vars, Options)</span> assigns a value to each variable <span class="c003">X</span> of the list <span class="c003">Vars</span> according to the list of labeling options given by <span class="c003">Options</span>. <span class="c003">Vars</span> can be also a single FD variable. This predicate is re-executable on backtracking.</p><p><span class="c009">FD labeling options</span>: <span class="c003">Options</span> 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"><a id="hevea_default995"></a><span class="c003">variable_method(V)</span>: specifies the heuristics to select the variable to enumerate:<ul class="itemize"><li class="li-itemize"><a id="hevea_default996"></a><span class="c003">standard</span>: no heuristics, the leftmost variable is selected.</li><li class="li-itemize"><a id="hevea_default997"></a><span class="c003">first_fail</span> (or <span class="c003">ff</span>): 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"><a id="hevea_default998"></a><span class="c003">most_constrained</span>: like <span class="c003">first_fail</span> but when several variables have the same number of elements selects the variable that appears in most constraints.</li><li class="li-itemize"><a id="hevea_default999"></a><span class="c003">smallest</span>: 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"><a id="hevea_default1000"></a><span class="c003">largest</span>: 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"><a id="hevea_default1001"></a><span class="c003">max_regret</span>: 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"><a id="hevea_default1002"></a><span class="c003">random</span>: selects randomly a variable. Each variable is chosen only once.</li></ul><p>The default value is <span class="c003">standard</span>.</p></li><li class="li-itemize"><a id="hevea_default1003"></a><span class="c003">reorder(true/false)</span>: specifies if the variable heuristics should dynamically reorder the list of variable (<span class="c003">true</span>) or not (<span class="c003">false</span>). Dynamic reordering is generally more efficient but in some cases a static ordering is faster. The default value is <span class="c003">true</span>.</li><li class="li-itemize"><a id="hevea_default1004"></a><span class="c003">value_method(V)</span>: specifies the heuristics to select the value to assign to the chosen variable:<ul class="itemize"><li class="li-itemize"><a id="hevea_default1005"></a><span class="c003">min</span>: enumerates the values from the smallest to the greatest (default).</li><li class="li-itemize"><a id="hevea_default1006"></a><span class="c003">max</span>: enumerates the values from the greatest to the smallest.</li><li class="li-itemize"><a id="hevea_default1007"></a><span class="c003">middle</span>: enumerates the values from the middle to the bounds.</li><li class="li-itemize"><a id="hevea_default1008"></a><span class="c003">bounds</span>: enumerates the values from the bounds to the middle.</li><li class="li-itemize"><a id="hevea_default1009"></a><span class="c003">random</span>: enumerates the values randomly. Each value is tried only once.</li><li class="li-itemize"><a id="hevea_default1010"></a><span class="c003">bisect</span>: recursively creates a choice between <span class="c003">X #=< M</span> and <span class="c003">X #> M</span>, where <span class="c003">M</span> is the midpoint of the domain of the variable. Values are thus tried from the smallest to the greatest. This is also known as <span class="c008">domain splitting</span>.</li></ul><p>The default value is <span class="c003">min</span>.</p></li><li class="li-itemize"><a id="hevea_default1011"></a><span class="c003">backtracks(B)</span>: unifies <span class="c003">B</span> with the number of backtracks during the enumeration.</li></ul><p><span class="c003">fd_labeling(Vars)</span> is equivalent to <span class="c003">fd_labeling(Vars, [])</span>.</p><p><span class="c003">fd_labelingff(Vars)</span> is equivalent to <span class="c003">fd_labeling(Vars, [variable_method(ff)])</span>.</p><p><span class="c009">Errors</span></p><table class="c001 cellpading0"><tr><td class="hbar" colspan=3></td></tr> <tr><td class="c018"> <span class="c003">Vars</span> is a partial list or a list with an element <span class="c003">E</span> which is a variable</td><td class="c013">  </td><td class="c018"><span class="c003">instantiation_error</span> </td></tr> <tr><td class="hbar" colspan=3></td></tr> <tr><td class="c018"> <span class="c003">Vars</span> is neither a partial list nor a list</td><td class="c013">  </td><td class="c018"><span class="c003">type_error(list, Vars)</span> </td></tr> <tr><td class="hbar" colspan=3></td></tr> <tr><td class="c018"> an element <span class="c003">E</span> of the <span class="c003">Vars</span> list is neither a variable nor an integer nor an FD variable</td><td class="c013">  </td><td class="c018"><span class="c003">type_error(fd_variable, E)</span> </td></tr> <tr><td class="hbar" colspan=3></td></tr> <tr><td class="c018"> <span class="c003">Options</span> is a partial list or a list with an element <span class="c003">E</span> which is a variable</td><td class="c013">  </td><td class="c018"><span class="c003">instantiation_error</span> </td></tr> <tr><td class="hbar" colspan=3></td></tr> <tr><td class="c018"> <span class="c003">Options</span> is neither a partial list nor a list</td><td class="c013">  </td><td class="c018"><span class="c003">type_error(list, Options)</span> </td></tr> <tr><td class="hbar" colspan=3></td></tr> <tr><td class="c018"> an element <span class="c003">E</span> of the <span class="c003">Options</span> list is neither a variable nor a labeling option</td><td class="c013">  </td><td class="c018"><span class="c003">domain_error(fd_labeling_option, E)</span> </td></tr> <tr><td class="hbar" colspan=3></td></tr> </table><p><span class="c009">Portability</span></p><p>GNU Prolog predicates.</p> <hr class="c011"> Copyright (C) 1999-2013 Daniel Diaz Verbatim copying and distribution of this entire article is permitted in any medium, provided this notice is preserved. <a href="index.html#copyright">More about the copyright</a> <hr> <a href="gprolog062.html"><img src="previous_motif.gif" alt="Previous"></a> <a href="gprolog054.html"><img src="contents_motif.gif" alt="Up"></a> <a href="gprolog064.html"><img src="next_motif.gif" alt="Next"></a> </body> </html>
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