我正在尝试使用CBC解算器（版本）解决pyomo（ Pyomo 5.3（Linux 3.10.0-514.26.2.el7.x86_64上的CPython 2.7.13））的优化问题：2.9.8 ）并指定求解器的时间限制为60秒。解算器正在获得一个可行的解决方案（-1415.8392），但显然还不是最佳（-1415.84），如下所示。
在时间限制结束后，模型似乎以错误代码退出。我想在指定的时间内使用CBC打印或获取可行解决方案的所有变量的值。或者，如果Model获得最佳解决方案的99％值，我可以设置任何其他方式来退出并打印可行解决方案。
错误代码发布在下面。
Cbc0004I Integer solution of -1415.8392 found after 357760 iterations and 29278 nodes (47.87 seconds)
Cbc0010I After 30000 nodes, 6350 on tree, -1415.8392 best solution, best possible -1415.84 (48.87 seconds)
Cbc0010I After 31000 nodes, 6619 on tree, -1415.8392 best solution, best possible -1415.84 (50.73 seconds)
Cbc0010I After 32000 nodes, 6984 on tree, -1415.8392 best solution, best possible -1415.84 (52.49 seconds)
Cbc0010I After 33000 nodes, 7384 on tree, -1415.8392 best solution, best possible -1415.84 (54.31 seconds)
Cbc0010I After 34000 nodes, 7419 on tree, -1415.8392 best solution, best possible -1415.84 (55.73 seconds)
Cbc0010I After 35000 nodes, 7824 on tree, -1415.8392 best solution, best possible -1415.84 (57.37 seconds)
Traceback (most recent call last):
File "model_final.py", line 392, in
solver.solve(model, timelimit = 60*1, tee=True)
File "/home/aditya/0r/lib/python2.7/site-packages/pyomo/opt/base/solvers.py", line 655, in solve
default_variable_value=self._default_variable_value)
File "/home/aditya/0r/lib/python2.7/site-packages/pyomo/core/base/PyomoModel.py", line 242, in load_from
% str(results.solver.status))
ValueError: Cannot load a SolverResults object with bad status: error
当我使用与pyomo /usr/bin/cbc -sec 60 -printingOptions all -import /tmp/tmpJK1ieR.pyomo.lp -import -stat=1 -solve -solu /tmp/tmpJK1ieR.pyomo.soln相同的命令行参数手动运行pyomo生成的模型时，它似乎正常退出并写入解决方案，如下所示。
Cbc0010I After 35000 nodes, 7824 on tree, -1415.8392 best solution, best possible -1415.84 (57.06 seconds) Cbc0038I Full problem 205 rows 289 columns, reduced to 30 rows 52 columns Cbc0010I After 36000 nodes, 8250 on tree, -1415.8392 best solution, best possible -1415.84 (58.73 seconds) Cbc0020I Exiting on maximum time Cbc0005I Partial search - best objective -1415.8392 (best possible -1415.84), took 464553 iterations and 36788 nodes (60.11 seconds) Cbc0032I Strong branching done 15558 times (38451 iterations), fathomed 350 nodes and fixed 2076 variables Cbc0035I Maximum depth 203, 5019 variables fixed on reduced cost Cbc0038I Probing was tried 31933 times and created 138506 cuts of which 0 were active after adding rounds of cuts (4.431 seconds) Cbc0038I Gomory was tried 30898 times and created 99534 cuts of which 0 were active after adding rounds of cuts (4.855 seconds) Cbc0038I Knapsack was tried 30898 times and created 12926 cuts of which 0 were active after adding rounds of cuts (8.271 seconds) Cbc0038I Clique was tried 100 times and created 0 cuts of which 0 were active after adding rounds of cuts (0.000 seconds) Cbc0038I MixedIntegerRounding2 was tried 30898 times and created 13413 cuts of which 0 were active after adding rounds of cuts (3.652 seconds) Cbc0038I FlowCover was tried 100 times and created 4 cuts of which 0 were active after adding rounds of cuts (0.019 seconds) Cbc0038I TwoMirCuts was tried 30898 times and created 15292 cuts of which 0 were active after adding rounds of cuts (2.415 seconds) Cbc0038I Stored from first was tried 30898 times and created 15734 cuts of which 0 were active after adding rounds of cuts (0.000 seconds) Cbc0012I Integer solution of -1411.9992 found by Reduced search after 467825 iterations and 36838 nodes (60.12 seconds) Cbc0020I Exiting on maximum time Cbc0005I Partial search - best objective -1411.9992 (best possible -1415.4522), took 467825 iterations and 36838 nodes (60.12 seconds) Cbc0032I Strong branching done 476 times (1776 iterations), fathomed 1 nodes and fixed 18 variables Cbc0035I Maximum depth 21, 39 variables fixed on reduced cost Cuts at root node changed objective from -1484.12 to -1415.45 Probing was tried 133 times and created 894 cuts of which 32 were active after adding rounds of cuts (0.060 seconds) Gomory was tried 133 times and created 1642 cuts of which 0 were active after adding rounds of cuts (0.047 seconds) Knapsack was tried 133 times and created 224 cuts of which 0 were active after adding rounds of cuts (0.083 seconds) Clique was tried 100 times and created 0 cuts of which 0 were active after adding rounds of cuts (0.001 seconds) MixedIntegerRounding2 was tried 133 times and created 163 cuts of which 0 were active after adding rounds of cuts (0.034 seconds) FlowCover was tried 100 times and created 5 cuts of which 0 were active after adding rounds of cuts (0.026 seconds) TwoMirCuts was tried 133 times and created 472 cuts of which 0 were active after adding rounds of cuts (0.021 seconds) ImplicationCuts was tried 25 times and created 41 cuts of which 0 were active after adding rounds of cuts (0.003 seconds) Result - Stopped on time limit Objective value: -1411.99922848 Lower bound: -1415.452 Gap: 0.00 Enumerated nodes: 36838 Total iterations: 467825 Time (CPU seconds): 60.13 Time (Wallclock seconds): 60.98 Total time (CPU seconds): 60.13 (Wallclock seconds): 61.01
CBC解决方案文件的前几行是：
Stopped on time - objective value -1411.99922848
0 c_e_x1454_ 0 0
1 c_e_x1455_ 0 0
2 c_e_x1456_ 0 0
3 c_e_x1457_ 0 0
4 c_e_x1458_ 0 0
5 c_e_x1459_ 0 0
6 c_e_x1460_ 0 0
7 c_e_x1461_ 0 0
8 c_e_x1462_ 0 0
有谁能告诉我如何在不产生任何错误的情况下获取这些值？
提前致谢。
答案 0 :(得分：0)
您可以尝试设置绑定间隙容差，以便接受其他答案。如果找到可行的解决方案，我很惊讶解算器状态会返回错误。你能打印出整个结果对象吗？
答案 1 :(得分：0)
创建了拉取请求https://github.com/Pyomo/pyomo/pull/265来解决此问题。
对于那些立即想要补丁的人：
在档案 pyomo / solvers / plugins / solvers / CBCplugin.py
@@ -264,7 +264,8 @@ def _check_and_escape_options(options):
cmd.append('-AMPL')
if self._timelimit is not None and self._timelimit > 0.0:
- cmd.extend(['-sec', str(self._timelimit)])
+ cmd.extend(['-sec', str(self._timelimit - 1 )])
+ cmd.extend(['-timeMode', "elapsed"])
if "debug" in self.options:
cmd.extend(["-log","5"])
for key, val in _check_and_escape_options(self.options):
@@ -276,7 +277,8 @@ def _check_and_escape_options(options):
#"-stat"])
else:
if self._timelimit is not None and self._timelimit > 0.0:
- cmd.extend(['-sec', str(self._timelimit)])
+ cmd.extend(['-sec', str(self._timelimit - 1 )])
+ cmd.extend(['-timeMode', "elapsed"])
if "debug" in self.options:
cmd.extend(["-log","5"])
# these must go after options that take a value
timelimit设置为比提供的选项低1秒，以确保在pyutilib.subprocess.processmngr检查退出代码之前CBC进程有时间正确退出。在我的测试运行中，进程管理器在T + 0.02秒检查退出状态，CBC进程通常在T + 0.1秒后退出。
还更改了CBC代码，使用默认CPU秒的wallclock秒，因为进程管理器也在检查相同内容。