Module: ppl/ppl Branch: pip Commit: b326ccf6d4297944eb51347295a37d492534400e URL: http://www.cs.unipr.it/git/gitweb.cgi?p=ppl/ppl.git;a=commit;h=b326ccf6d4297...
Author: François Galea francois.galea@uvsq.fr Date: Thu Nov 19 15:20:58 2009 +0100
Added a rule to the cut methods to always choose the simplest parametric part.
This tends to provide simpler solution trees on some problems.
---
src/PIP_Tree.cc | 52 +++++++++++++++++++++++++++++++++++++++++++++------- 1 files changed, 45 insertions(+), 7 deletions(-)
diff --git a/src/PIP_Tree.cc b/src/PIP_Tree.cc index 138a215..e868427 100644 --- a/src/PIP_Tree.cc +++ b/src/PIP_Tree.cc @@ -1736,14 +1736,36 @@ PIP_Solution_Node::solve(PIP_Tree_Node*& parent_ref, PPL_DIRTY_TEMP_COEFFICIENT(mod); if (problem.control_parameters[PIP_CUTTING_STRATEGY] == PIP_CUTTING_STRATEGY_FIRST) { - /* Just choose the row corresponding to variable i */ - i = mapping[i]; + // Find the first row with simplest parametric part. + dimension_type best_i = n_a_d; + dimension_type best_pcount = n_a_d; + dimension_type pcount; + for (i_ = 0; i_ < num_vars; ++i_) { + if (basis[i_]) + continue; + i = mapping[i_]; + const Row& row_t = tableau.t[i]; + pcount = 0; + for (j = 0; j < num_params; ++j) { + mod_assign(mod, row_t[j], d); + if (mod != 0) + ++pcount; + } + if (pcount != 0 && (best_i == n_a_d || (pcount < best_pcount))) { + best_pcount = pcount; + best_i = i; + } + } + i = best_i; } else /* PIP_CUTTING_STRATEGY_DEEPEST */ { - /* Look for the row which will generate the "deepest" cut */ + /* Find the row with simplest parametric part which will generate + the "deepest" cut */ PPL_DIRTY_TEMP_COEFFICIENT(score); PPL_DIRTY_TEMP_COEFFICIENT(score2); - Coefficient best = 0; + Coefficient best_score = 0; dimension_type best_i = n_a_d; + dimension_type best_pcount = n_a_d; + dimension_type pcount; for (i_ = 0; i_ < num_vars; ++i_) { if (basis[i_]) continue; @@ -1751,10 +1773,13 @@ PIP_Solution_Node::solve(PIP_Tree_Node*& parent_ref, const Row& row_t = tableau.t[i]; const Row& row_s = tableau.s[i]; score = 0; + pcount = 0; for (j = 0; j < num_params; ++j) { mod_assign(mod, row_t[j], d); - if (mod != 0) + if (mod != 0) { score += d - mod; + ++pcount; + } } score2 = 0; for (j = 0; j < num_vars; ++j) { @@ -1762,8 +1787,21 @@ PIP_Solution_Node::solve(PIP_Tree_Node*& parent_ref, score2 += d - mod; } score *= score2; - if (best_i == n_a_d || score > best) { - best = score; + /* Choose row i if: + row i is non-integer + AND (no row has been chosen yet + OR row i has number of non-integer parameter + coefficients lower than the current best row + OR row i has the same number of non-integer parameter + coefficients as the current best row, and its score is + better) + */ + if (pcount != 0 + && (best_i == n_a_d + || (pcount < best_pcount) + || (pcount == best_pcount && score > best_score))) { + best_score = score; + best_pcount = pcount; best_i = i; } }