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Good morning Richard and list,<br>
<br>
you have two possibilities to tell SCIP which variables should be
prioritized (branched on/assigned first in the tree).<br>
<br>
1. The hard way: Assign a higher <b>branching priority</b>
(SCIPvarChgBranchPriority()) to some variables. All branching rules
and some of the primal heuristics will only consider fractional
branching candidates that have the highest priority. Lower priority
variables are excluded from the branching decision until there is no
high priority variable left. The default priority of all variables
is 0. Since the priority is an integer attribute of a variable, you
can in principle fix the variable order for SCIP to branch on, by
assigning unique priorities to every variable.<br>
<br>
2. The soft way: Assign a higher <b>branching factor</b>
(SCIPvarChgBranchFactor()) to fine-tune the scoring mechanism. If
your s variables (start times) have a branching priority of 10.0
(the default is 1.0, of course), they are much more likely to be
selected for branching, unless the (unweighted) branching score of
another variable (say, a job end variable e) is 10 times higher than
that of the best s variable.<br>
<br>
Branching enthusiasts may even mix 1. and 2. Let us know if you
experience a good impact with one of the above methods.<br>
<br>
Happy branching,<br>
Gregor<br>
<br>
<div class="moz-cite-prefix">Am 03.05.19 um 18:51 schrieb Levinson,
Richard J. (ARC-TI)[SGT, INC]:<br>
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<span><span style="font-family: Calibri, Helvetica,
sans-serif, Helvetica, EmojiFont, "Apple Color
Emoji", "Segoe UI Emoji", NotoColorEmoji,
"Segoe UI Symbol", "Android Emoji",
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</span></span></div>
<div id="divtagdefaultwrapper" dir="ltr" style="font-size: 12pt;
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<span><span style="font-family: Calibri, Helvetica,
sans-serif, Helvetica, EmojiFont, "Apple Color
Emoji", "Segoe UI Emoji", NotoColorEmoji,
"Segoe UI Symbol", "Android Emoji",
EmojiSymbols; font-size: 16px;">I'm looking for a way to
specify that some variables are the "primary" decision
variables to drive search, while other variables are
"dependent" variables, which</span><span
style="font-family: Calibri, Helvetica, sans-serif,
Helvetica, EmojiFont, "Apple Color Emoji",
"Segoe UI Emoji", NotoColorEmoji, "Segoe UI
Symbol", "Android Emoji", EmojiSymbols;
font-size: 16px;"> depend on the primary variables via
constraints, so that the dependent variable assignments
are made only after feasible assignments for the primary
variables have been found. </span><br>
<span style="font-family: Calibri, Helvetica, sans-serif,
Helvetica, EmojiFont, "Apple Color Emoji",
"Segoe UI Emoji", NotoColorEmoji, "Segoe UI
Symbol", "Android Emoji", EmojiSymbols;
font-size: 16px;"></span></span></div>
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Emoji", "Segoe UI Emoji", NotoColorEmoji,
"Segoe UI Symbol", "Android Emoji",
EmojiSymbols;">
<span><span style="font-family: Calibri, Helvetica,
sans-serif, Helvetica, EmojiFont, "Apple Color
Emoji", "Segoe UI Emoji", NotoColorEmoji,
"Segoe UI Symbol", "Android Emoji",
EmojiSymbols; font-size: 16px;"><br>
</span></span></div>
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"Segoe UI Symbol", "Android Emoji",
EmojiSymbols;">
<span style="font-size: 12pt;">Is there a way to tell SCIP </span><span
style="font-size: 12pt;">that some variables are considered
‘dependent’, i.e. they should not be considered as part of
the search space, but must be propagated using constraints
in the problem?</span><br>
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"Segoe UI Symbol", "Android Emoji",
EmojiSymbols;">
<br>
<span></span>
<p style="margin-top:0; margin-bottom:0">Or if there is no way
to specify that some variables should not be part of the
search space, is there an option to specify the
order/priority for assigning variables? So the solver<span
style="font-size: 12pt;"> searches first through the
domains of the primary (high priority) variables to find a
feasible solution before it searches for consistent
assignments for the dependent variables. </span><span
style="font-size: 12pt;"></span></p>
<p style="margin-top:0; margin-bottom:0"><br>
</p>
<p style="margin-top:0; margin-bottom:0">For example, we
may have variables s, e, d, representing a job's start, end,
and duration times, and we want to first search for feasible
assignments for s and e before applying the constraint that
e-s = d. </p>
<p style="margin-top:0; margin-bottom:0"><br>
</p>
<p style="margin-top:0; margin-bottom:0">Thank you,</p>
<p style="margin-top:0; margin-bottom:0"><br>
</p>
<p style="margin-top:0; margin-bottom:0"> Rich Levinson</p>
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<br>
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