Merge pull request #10 from abhosekar/master

mabdullahsoyturk · web-flow · commit 3e32c2935338 · 2025-07-18T16:39:45.000+03:00
tsp4 subtour identification improved using networkx
diff --git a/models/tsp4/tsp4.py b/models/tsp4/tsp4.py
@@ -21,6 +21,7 @@
 from __future__ import annotations
 
 from pathlib import Path
+import networkx as nx
 
 import gamspy.math as gams_math
 from gamspy import (
@@ -167,9 +168,6 @@ def main():
     # Parameter
     cutcoeff = Parameter(m, name="cutcoeff", domain=[cc, i, j])
     rhs = Parameter(m, name="rhs", domain=cc)
-    nosubtours = Parameter(
-        m, name="nosubtours", description="number of subtours"
-    )
 
     # Equation
     cut = Equation(m, name="cut", domain=cc, description="dynamic cuts")
@@ -190,51 +188,22 @@ def main():
     curcut[cc].where[Ord(cc) == 1] = True
 
     for ccc_loop in ccc.toList():
-        #  initialize
-        fromi[i].where[Ord(i) == 1] = True  # turn first element on
-        tt[t].where[Ord(t) == 1] = True  # turn first element on
-        tour[i, j, t] = False
-        visited[i] = False
-
-        for _ in i.toList():
-            nextj[j].where[x.l[fromi, j] > 0.5] = (
-                True  # check x.l(fromi,j) = 1 would be dangerous
-            )
-            tour[fromi, nextj, tt] = True  # store in table
-            visited[fromi] = True  # mark city 'fromi' as visited
-            fromi[j] = nextj[j]
-
-            if nextj.toList()[0] in visited.toList():  # if already visited...
-                tt[t] = tt[t - 1]
-                for ix_loop in ix.toList():
-                    if (
-                        ix_loop in visited.toList()
-                    ):  # find starting point of new subtour
-                        continue
-                    fromi[ix_loop] = True
-
-        nosubtours[...] = Sum(t, gams_math.Max(0, Smax(tour[i, j, t], 1)))
-
-        if nosubtours.toValue() == 1:  # done: no subtours
+        G = nx.DiGraph()
+        G.add_nodes_from(i.getUELs())
+        x_filtered = x.records[x.records['level'] > 0.5].loc[:, :"level"]
+        edges =  list(zip(x_filtered['ii'], x_filtered['jj']))
+        G.add_edges_from(edges)
+        S = [G.subgraph(c).copy() for c in nx.strongly_connected_components(G)]
+
+        nosubtours = len(S)
+        if nosubtours == 1:  # done: no subtours
             break
 
-        # introduce cut
-        for idx, t_loop in enumerate(t.toList()):
-            if idx + 1 > nosubtours.toValue():
-                continue
+        for s in S:
             rhs[curcut] = -1
-
-            for i_loop, j_loop, t_loop2, _ in tour.records.itertuples(
-                index=False
-            ):
-                if t_loop2 != t_loop:
-                    continue
-
-                cutcoeff[curcut, i_loop, j_loop].where[
-                    x.l[i_loop, j_loop] > 0.5
-                ] = 1
-                # not needed due to nature of assignment constraints
-                #        cutcoeff(curcut, i, j)$(x.l[i,j] < 0.5) = -1
+            for u, v in s.edges():
+                if x.l[u, v].records > 0.5:
+                    cutcoeff[curcut, i, j].where[i.sameAs(u) & j.sameAs(v)] = 1
                 rhs[curcut] = rhs[curcut] + 1
             allcuts[curcut] = True  # include this cut in set
             curcut[cc] = curcut[cc - 1]
@@ -244,10 +213,10 @@ def main():
             "Cut: ",
             ccc_loop,
             "\t\t # of subtours remaining: ",
-            nosubtours.toValue() - 1,
+            nosubtours - 1,
         )
 
-    if nosubtours.toValue() != 1:
+    if nosubtours != 1:
         raise GamspyException("Too many cuts needed")
 
     print("No subtours remaining. Solution found!!\n")
