def step(g, loops, feas_elims, ub, stats):
# Solve relaxation with the cycle matrix of loops. This solution
# MUST BE rigorous.
relax_elims, lb = solve_relaxation(g, loops, stats)
assert lb <= ub
if lb == ub:
log('*** Optimal solution found ***')
return None, None, feas_elims, ub
#
g_ruins = g.copy()
for e in relax_elims:
g_ruins.remove_edge(*e)
#
if nx.is_directed_acyclic_graph(g_ruins):
log('*** Relaxation became feasible ***')
return None, None, relax_elims, lb,
#
log()
log('Remaining graph')
info(g_ruins, log=log)
#
# Get the missed edges and the ruins of the relaxation: We need new
# candidate loops. The missed_edges does not have to be rigorous. We may
# also improve the currently best feasible solution.
missed = missed_edges(g_ruins)
assert missed
new_feas_elims = relax_elims + missed
new_ub = sum(g[u][v]['weight'] for u, v in new_feas_elims)
assert new_ub > lb
if new_ub < ub:
log('Improved UB: {} -> {}'.format(ub, new_ub))
ub, feas_elims = new_ub, new_feas_elims
double_check(g, ub, feas_elims, is_labeled=True, log=log)
return missed, g_ruins, feas_elims, ub
def solve_triangle_inequalities(g, stats, feasible_sol):
iteratively_remove_runs_and_bypasses(g)
# The above simplification removes edges, but the d['orig_edges'] still
# refers to these edges. As a result, the double_check calls in this module
# and in mfes will fail in the cost calculation, when trying to access
# those not present edges to figure out their edge weights. So we have to
# replace d['orig_edges'] appropriately and undo this at the end of this
# function. Additionally, as runs are removed, new edges are introduced
# that are not in the original graph. It is much simpler to just relabel
# the graph and then undo it on the elimination order.
origedges_map = get_orig_edges_map(g)
#
model, y = build_lp(g, feasible_sol)
start = time()
success = solve_ilp(model, stats)
end = time()
print('Overall solution time: {0:0.1f} s'.format(end - start))
assert success, 'Solver failures are not handled at the moment...'
cost = int(round(model.getObjective().getValue()))
elim_order = recover_order(model, y, len(g))
elims = get_torn_edges(g, elim_order)
# Done. Now undo the d['orig_edges'] mess.
final_elims = []
for edge in elims:
final_elims.extend(origedges_map[edge])
double_check(g, cost, elims, is_labeled=True)
return final_elims, cost
def simplify(g):
print('Nodes:', g.number_of_nodes())
print('Edges:', g.number_of_edges())
cycles = list(nx.simple_cycles(g)) # <-
print('Loops:', len(cycles)) # <-
orig_input = deepcopy(g)
sccs = split_to_nontrivial_sccs(g)
# Clean-up the new smaller SCCs without splitting them
for sc in sccs:
iteratively_remove_runs_and_bypasses(sc)
#
running_cost, elims = 0, [ ]
info_after_cleanup(sccs, running_cost)
#
clean_sccs = [ ]
for scc in sccs:
plot(scc, prog='sfdp')
new_sccs, running_cost = try_neighborhood(scc, running_cost, elims)
clean_sccs.extend( new_sccs )
# check what remains
if clean_sccs:
info_after_cleanup(clean_sccs, running_cost)
print(sorted(n for n in clean_sccs[0]))
dbg_dump_as_edgelist(clean_sccs[0])
else:
print('The simplifier eliminated the whole input at cost', running_cost)
double_check(orig_input, running_cost, elims)
print('Chosen:', elims)
def solve_with_pcm(g, stats, feasible_sol):
g_orig = g.copy()
iteratively_remove_runs_and_bypasses(g) # d['orig_edges'] mess,
origedges_map = get_orig_edges_map(g) # see explanation in grb_pcm.py
#
# FIXME It assumes that we only have a single SCC
elims, ub = feasible_solution(g) if feasible_sol is None else feasible_sol
# A shortest path around each edge, see grb_pcm.py for possible improvements
loops = initial_loop_set(g)
print('Initial cycle matrix size:', len(loops))
# Build the model, set the elims as initial solution
m, vrs = build_ilp(g, loops, elims)
# Put into the model dict everything we need in the callback
m._vrs, m._g, m._loops, m._elims, m._ub = vrs, g, loops, elims, ub
#
solve(m, stats)
#
loops, elims, ub = m._loops, m._elims, m._ub
print('Final cycle matrix size:', len(loops))
#simplify(g, loops, elims, ub)
#run_IIS(g, loops, elims, ub)
# Done. Now undo the d['orig_edges'] mess.
final_elims = []
for edge in elims:
final_elims.extend(origedges_map[edge])
double_check(g_orig, ub, final_elims, is_labeled=True, log=print)
return final_elims, ub, loops
def rigorous_mfes(subgraph, cutoff):
# It is just a convenience wrapper around solve_cm. Returns:
# (error msg, elims, obj, ncyc). The error message is empty iff successful.
success, edges_per_cycle = get_all_cycles(subgraph, cutoff)
if not success:
return 'Too many simple cycles in relaxed SCC', None, None, None
elims, objective = solve_cm(subgraph, edges_per_cycle)
if elims is None:
return 'Solver failure, giving up', None, None, None
assert objective > 0 # in an SCC at least...
double_check(subgraph, objective, elims)
return '', elims, objective, len(edges_per_cycle)
def solve_problem(g_orig, stats=None):
'Returns: [torn edges], cost.'
elims, cost = [], 0
for sc in noncopy_split_to_nontrivial_sccs(
g_orig.copy()): # <- Copy passed!
partial_elims, partial_cost = solve_with_pcm(sc, stats)
elims.extend(partial_elims)
cost += partial_cost
double_check(g_orig, cost, elims, is_labeled=True, log=log)
log('Input graph')
info(g_orig, log=log)
return elims, cost
def solve_problem(g_orig, stats=None, feasible_sol=None):
'Returns: [torn edges], cost.'
elims, cost = [], 0
for sc in noncopy_split_to_nontrivial_sccs(
g_orig.copy()): # <- Copy passed!
partial_elims, partial_cost = \
solve_triangle_inequalities(sc, stats, feasible_sol)
elims.extend(partial_elims)
cost += partial_cost
double_check(g_orig, cost, elims, is_labeled=True)
print('Input graph')
info_short(g_orig)
return elims, cost
def solve_problem(g_orig, stats, feasible_sol=None):
'Returns: [torn edges], cost.'
elims, cost = [], 0
g2 = g_orig.copy()
# Remove self-loops
for u, v, d in g_orig.selfloop_edges(data=True):
g2.remove_edge(u, v)
elims.append((u, v))
cost += d['weight']
cycle_matrix = []
# Make each SCC acyclic
for sc in noncopy_split_to_nontrivial_sccs(g2):
partial_elims, partial_cost, loops = solve_with_pcm(
sc, stats, feasible_sol)
elims.extend(partial_elims)
cost += partial_cost
cycle_matrix.extend(loops)
double_check(g_orig, cost, elims, is_labeled=True, log=log)
log('Input graph')
info(g_orig, log=log)
return elims, cost, cycle_matrix
def run_mfes_heuristic(g_input, try_one_cut=False, is_labeled=False):
# Set the edge attributes 'weight' and 'orig_edges' if necessary
g, copy_g = label_edges(g_input, is_labeled)
#
greedy_choice = no_lookahead if try_one_cut else with_lookahead
#
running_cost, elims = 0, []
sccs, running_cost = iterate_cleanup(g, running_cost, elims, copy_g)
info_after_cleanup(sccs, running_cost)
while True:
sccs_to_process = []
for sc in sccs:
log('-----------------------------------------------------------')
#distributions(sc)
new_state = greedy_choice(sc, running_cost, elims)
new_sccs, elims, running_cost = new_state
sccs_to_process.extend(new_sccs)
sccs = sccs_to_process
if len(sccs) == 0:
# Make sure that what we return is at least consistent
double_check(g_input, running_cost, elims, is_labeled, log=log)
return running_cost, elims
def extend_cm(m):
g, ub, ub2 = m._g, m._ub, int(round(m.cbGet(GRB.Callback.MIPSOL_OBJ)))
#if ub2 >= ub:
# return
log('Callback with obj: ', ub2)
#
relax_elims, new_feas_elims, missed_loops = get_solution(m)
if not missed_loops:
if ub2 < ub:
log('Relaxation became feasible and improved UB {} -> {}'.format(
ub, ub2))
m._elims, m._ub = relax_elims, ub2
double_check(g, ub2, relax_elims, is_labeled=True, log=log)
return
#
new_ub = sum(g[u][v]['weight'] for u, v in new_feas_elims)
if new_ub < ub:
log('Improved UB: {} -> {}'.format(ub, new_ub))
double_check(g, new_ub, new_feas_elims, is_labeled=True, log=log)
m._ub, m._elims = new_ub, new_feas_elims
#
extend_the_cycle_matrix(m, missed_loops)
