本文整理汇总了Python中pyscipopt.Model.chgVarType方法的典型用法代码示例。如果您正苦于以下问题：Python Model.chgVarType方法的具体用法？Python Model.chgVarType怎么用？Python Model.chgVarType使用的例子？那么恭喜您, 这里精选的方法代码示例或许可以为您提供帮助。您也可以进一步了解该方法所在类pyscipopt.Model的用法示例。
在下文中一共展示了Model.chgVarType方法的2个代码示例，这些例子默认根据受欢迎程度排序。您可以为喜欢或者感觉有用的代码点赞，您的评价将有助于系统推荐出更棒的Python代码示例。
示例1: solve_tsp
# 需要导入模块: from pyscipopt import Model [as 别名]
# 或者: from pyscipopt.Model import chgVarType [as 别名]
def solve_tsp(V,c):
"""solve_tsp -- solve the traveling salesman problem
- start with assignment model
- add cuts until there are no sub-cycles
Parameters:
- V: set/list of nodes in the graph
- c[i,j]: cost for traversing edge (i,j)
Returns the optimum objective value and the list of edges used.
"""
def addcut(cut_edges):
G = networkx.Graph()
G.add_edges_from(cut_edges)
Components = list(networkx.connected_components(G))
if len(Components) == 1:
return False
model.freeTransform()
for S in Components:
model.addCons(quicksum(x[i,j] for i in S for j in S if j>i) <= len(S)-1)
print("cut: len(%s) <= %s" % (S,len(S)-1))
return True
def addcut2(cut_edges):
G = networkx.Graph()
G.add_edges_from(cut_edges)
Components = list(networkx.connected_components(G))
if len(Components) == 1:
return False
model.freeTransform()
for S in Components:
T = set(V) - set(S)
print("S:",S)
print("T:",T)
model.addCons(quicksum(x[i,j] for i in S for j in T if j>i) +
quicksum(x[i,j] for i in T for j in S if j>i) >= 2)
print("cut: %s >= 2" % "+".join([("x[%s,%s]" % (i,j)) for i in S for j in T if j>i]))
return True
# main part of the solution process:
model = Model("tsp")
model.hideOutput() # silent/verbose mode
x = {}
for i in V:
for j in V:
if j > i:
x[i,j] = model.addVar(ub=1, name="x(%s,%s)"%(i,j))
for i in V:
model.addCons(quicksum(x[j,i] for j in V if j < i) + \
quicksum(x[i,j] for j in V if j > i) == 2, "Degree(%s)"%i)
model.setObjective(quicksum(c[i,j]*x[i,j] for i in V for j in V if j > i), "minimize")
EPS = 1.e-6
isMIP = False
while True:
model.optimize()
edges = []
for (i,j) in x:
if model.getVal(x[i,j]) > EPS:
edges.append( (i,j) )
if addcut(edges) == False:
if isMIP: # integer variables, components connected: solution found
break
model.freeTransform()
for (i,j) in x: # all components connected, switch to integer model
model.chgVarType(x[i,j], "B")
isMIP = True
return model.getObjVal(),edges示例2: solve_tsp
# 需要导入模块: from pyscipopt import Model [as 别名]
# 或者: from pyscipopt.Model import chgVarType [as 别名]
def solve_tsp(V,c):
"""solve_tsp -- solve the traveling salesman problem
- start with assignment model
- check flow from a source to every other node;
- if no flow, a sub-cycle has been found --> add cut
- otherwise, the solution is optimal
Parameters:
- V: set/list of nodes in the graph
- c[i,j]: cost for traversing edge (i,j)
Returns the optimum objective value and the list of edges used.
"""
def addcut(X):
for sink in V[1:]:
mflow = maxflow(V,X,V[0],sink)
mflow.optimize()
f,cons = mflow.data
if mflow.ObjVal < 2-EPS: # no flow to sink, can add cut
break
else:
return False
#add a cut/constraint
CutA = set([V[0]])
for i in cons:
if cons[i].Pi <= -1+EPS:
CutA.add(i)
CutB = set(V) - CutA
main.addCons(
quicksum(x[i,j] for i in CutA for j in CutB if j>i) + \
quicksum(x[j,i] for i in CutA for j in CutB if j<i) >= 2)
print("mflow:",mflow.getObjVal(),"cut:",CutA,"+",CutB,">= 2")
print("mflow:",mflow.getObjVal(),"cut:",[(i,j) for i in CutA for j in CutB if j>i],"+",[(j,i) for i in CutA for j in CutB if j<i],">= 2")
return True
def isMIP(x):
for var in x:
if var.vtype == "CONTINUOUS":
return False
return True
# main part of the solution process:
main = Model("tsp")
x = {}
for i in V:
for j in V:
if j > i:
x[i,j] = main.addVar(ub=1, vtype="C", name="x(%s,%s)"%(i,j))
for i in V:
main.addCons(quicksum(x[j,i] for j in V if j < i) + \
quicksum(x[i,j] for j in V if j > i) == 2, "Degree(%s)"%i)
main.setObjective(quicksum(c[i,j]*x[i,j] for i in V for j in V if j > i), "minimize")
while True:
main.optimize()
z = main.getObjVal()
X = {}
for (i,j) in x:
if main.getVal(x[i,j]) > EPS:
X[i,j] = main.getVal(x[i,j])
if addcut(X) == False: # i.e., components are connected
if isMIP(): # integer variables, components connected: solution found
break
for (i,j) in x: # all components connected, switch to integer model
main.chgVarType(x[i,j], "BINARY")
# process solution
edges = []
for (i,j) in x:
if main.getVal(x[i,j]) > EPS:
edges.append((i,j))
return main.getObjVal(),edges