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Merge remote-tracking branch 'upstream/hotfixes' into release
2 parents 722eaee + 5486e7f commit 3aa036c

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‎pm4py/objects/petri_net/utils/murata.py‎

Lines changed: 120 additions & 75 deletions
Original file line numberDiff line numberDiff line change
@@ -33,10 +33,18 @@ def apply_reduction(
3333
net: PetriNet, im: Marking, fm: Marking
3434
) -> Tuple[PetriNet, Marking, Marking]:
3535
"""
36-
Apply the Murata reduction to an accepting Petri net, removing the structurally redundant places.
36+
Apply the Murata reduction to an accepting Petri net, removing structurally redundant (implicit) places.
3737
38-
The implementation follows the Berthelot algorithm as in:
39-
https://svn.win.tue.nl/repos/prom/Packages/Murata/Trunk/src/org/processmining/algorithms/BerthelotAlgorithm.java
38+
This implementation follows the (Berthelot) implicit-place check by searching, via ILP,
39+
for a place-flow f = a_p * p - Σ a_q * q (a_p >= 1, a_q >= 0) such that:
40+
41+
(1) f is a P-invariant (flow): a_p*C(p,t) - Σ a_q*C(q,t) = 0 for all transitions t
42+
where C(p,t) = Post(p,t) - Pre(p,t)
43+
44+
(2) a_p*Pre(p,t) - Σ a_q*Pre(q,t) <= k for all transitions t
45+
with k = a_p*M0(p) - Σ a_q*M0(q), and k >= 0
46+
47+
If such a solution exists, the candidate place is implicit and can be removed without changing behavior.
4048
4149
Parameters
4250
---------------
@@ -50,101 +58,137 @@ def apply_reduction(
5058
Returns
5159
--------------
5260
net
53-
Petri net
61+
Reduced Petri net
5462
im
55-
Initial marking
63+
Initial marking (unchanged)
5664
fm
57-
Final marking
65+
Final marking (unchanged)
5866
"""
5967
places = sorted(list(net.places), key=lambda x: x.name)
60-
place_index = {p: i for i, p in enumerate(places)}
61-
n_places = len(places)
62-
6368
redundant = set()
6469

70+
# Choose solver backend
71+
proposed_solver = solver.SCIPY
72+
if importlib.util.find_spec("pulp"):
73+
proposed_solver = solver.PULP
74+
else:
75+
if constants.SHOW_INTERNAL_WARNINGS:
76+
warnings.warn(
77+
"solution from scipy may be unstable. Please install PuLP (pip install pulp) for fully reliable results."
78+
)
79+
6580
for place in places:
81+
# Skip already proven redundant places
82+
if place in redundant:
83+
continue
84+
6685
# Skip places in the initial or final markings
6786
if place in im or place in fm:
6887
continue
6988

89+
# Work on the "current" net as if previously found redundant places were removed:
90+
active_places = [p for p in places if p not in redundant]
91+
active_places = sorted(active_places, key=lambda x: x.name)
92+
place_index = {p: i for i, p in enumerate(active_places)}
93+
94+
n_places = len(active_places)
95+
n_vars = n_places + 1 # last variable is k
96+
k_idx = n_vars - 1
97+
7098
Aeq = []
7199
Aub = []
72100
beq = []
73101
bub = []
74102

75-
# first constraint
76-
constraint = [0] * (n_places + 1)
77-
for p2 in im:
78-
if p2 not in redundant:
79-
if p2 == place:
80-
constraint[place_index[p2]] = im[p2]
81-
else:
82-
constraint[place_index[p2]] = -im[p2]
83-
constraint[-1] = -1
84-
Aeq.append(constraint)
103+
# ---------------------------------------------------------------------
104+
# (A) k = a_p*M0(p) - Σ a_q*M0(q)
105+
# => a_p*M0(p) - Σ a_q*M0(q) - k = 0
106+
# ---------------------------------------------------------------------
107+
eq = [0] * n_vars
108+
for p2 in active_places:
109+
m0 = im[p2] if p2 in im else 0
110+
if m0 == 0:
111+
continue
112+
if p2 == place:
113+
eq[place_index[p2]] += m0
114+
else:
115+
eq[place_index[p2]] -= m0
116+
eq[k_idx] = -1
117+
Aeq.append(eq)
85118
beq.append(0)
86119

87-
# second constraints
120+
# ---------------------------------------------------------------------
121+
# (B) Flow constraints: for all transitions t,
122+
# a_p*C(p,t) - Σ a_q*C(q,t) = 0
123+
# where C(p,t)=Post(p,t)-Pre(p,t)
124+
# ---------------------------------------------------------------------
88125
for trans in net.transitions:
89-
constraint = [0] * (n_places + 1)
126+
pre = {}
127+
post = {}
90128

91129
for arc in trans.in_arcs:
92-
p2 = arc.source
93-
if p2 not in redundant:
94-
if p2 == place:
95-
constraint[place_index[p2]] = arc.weight
96-
else:
97-
constraint[place_index[p2]] = -arc.weight
98-
99-
constraint[-1] = -1
100-
Aub.append(constraint)
101-
bub.append(0)
102-
103-
# third constraints (FIXED SIGNS)
104-
for trans in net.transitions:
105-
constraint = [0] * (n_places + 1)
130+
src = arc.source
131+
if src in place_index:
132+
pre[src] = pre.get(src, 0) + arc.weight
106133

107134
for arc in trans.out_arcs:
108-
p2 = arc.target
109-
if p2 not in redundant:
110-
# FIX: candidate place must have +weight, other places -weight
111-
# (the previous implementation inverted these signs)
112-
if p2 == place:
113-
constraint[place_index[p2]] = arc.weight
114-
else:
115-
constraint[place_index[p2]] = -arc.weight
116-
117-
Aub.append(constraint)
118-
bub.append(0)
119-
120-
# fourth constraint
121-
for p2 in places:
122-
if p2 not in redundant:
123-
constraint = [0] * (n_places + 1)
124-
constraint[place_index[p2]] = -1
125-
Aub.append(constraint)
135+
tgt = arc.target
136+
if tgt in place_index:
137+
post[tgt] = post.get(tgt, 0) + arc.weight
138+
139+
eq = [0] * n_vars
140+
for p2 in active_places:
141+
c_val = post.get(p2, 0) - pre.get(p2, 0)
142+
if c_val == 0:
143+
continue
126144
if p2 == place:
127-
bub.append(-1)
145+
eq[place_index[p2]] += c_val
128146
else:
129-
bub.append(0)
130-
131-
# fifth constraint
132-
constraint = [0] * (n_places + 1)
133-
constraint[-1] = -1
134-
Aub.append(constraint)
135-
bub.append(0)
136-
137-
c = [1] * (n_places + 1)
138-
integrality = [1] * (n_places + 1)
139-
140-
proposed_solver = solver.SCIPY
141-
if importlib.util.find_spec("pulp"):
142-
proposed_solver = solver.PULP
143-
else:
144-
if constants.SHOW_INTERNAL_WARNINGS:
145-
warnings.warn(
146-
"solution from scipy may be unstable. Please install PuLP (pip install pulp) for fully reliable results."
147-
)
147+
eq[place_index[p2]] -= c_val
148+
# k has coefficient 0 here
149+
Aeq.append(eq)
150+
beq.append(0)
151+
152+
# ---------------------------------------------------------------------
153+
# (C) Implicitness inequalities: for all transitions t,
154+
# a_p*Pre(p,t) - Σ a_q*Pre(q,t) - k <= 0
155+
# ---------------------------------------------------------------------
156+
for trans in net.transitions:
157+
ineq = [0] * n_vars
158+
for arc in trans.in_arcs:
159+
p2 = arc.source
160+
if p2 not in place_index:
161+
continue
162+
if p2 == place:
163+
ineq[place_index[p2]] += arc.weight
164+
else:
165+
ineq[place_index[p2]] -= arc.weight
166+
ineq[k_idx] = -1
167+
Aub.append(ineq)
168+
bub.append(0)
169+
170+
# ---------------------------------------------------------------------
171+
# (D) Variable lower bounds:
172+
# a_p >= 1, a_q >= 0, k >= 0
173+
# Implemented as -a <= b
174+
# ---------------------------------------------------------------------
175+
for p2 in active_places:
176+
ineq = [0] * n_vars
177+
ineq[place_index[p2]] = -1
178+
Aub.append(ineq)
179+
if p2 == place:
180+
bub.append(-1) # -a_p <= -1 -> a_p >= 1
181+
else:
182+
bub.append(0) # -a_q <= 0 -> a_q >= 0
183+
184+
ineq = [0] * n_vars
185+
ineq[k_idx] = -1
186+
Aub.append(ineq)
187+
bub.append(0) # -k <= 0 -> k >= 0
188+
189+
# Objective (any feasible solution is enough; minimize sum to keep it small)
190+
c = [1] * n_vars
191+
integrality = [1] * n_vars
148192

149193
xx = solver.apply(
150194
c,
@@ -161,7 +205,8 @@ def apply_reduction(
161205
):
162206
redundant.add(place)
163207

164-
for place in redundant:
165-
net = remove_place(net, place)
208+
# Remove redundant places (deterministic order)
209+
for pl in sorted(list(redundant), key=lambda x: x.name):
210+
net = remove_place(net, pl)
166211

167212
return net, im, fm

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