5

after setting the objective function and constraints, i use

prob.solve()
print prob.solution.get_objective_value()

actually, I just want to print the objective value, however, it displays a lot of information of cplex, 

Tried aggregator 1 time.
LP Presolve eliminated 5 rows and 1 columns.
All rows and columns eliminated.
Presolve time = -0.00 sec. (0.00 ticks)
0.5

I just want to display the last line 0.5, how to avoid printing other information by Cplex? Thank you in advance.

David Nehme
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ilovecp3
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3 Answers3

10

cplex specifies 3 output streams: log, error, warning and results. You can disable the output with the commands. set_xxx_stream(None). In your example,

prob.set_log_stream(None)
prob.set_error_stream(None)
prob.set_warning_stream(None)
prob.set_results_stream(None)

will disable all output. You can also specify an output file, instead of None. There are also several parameters that you can set to control the verbosity of the cplex output, but this is the best way to prevent cplex from printing anything.

David Nehme
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2

You can adjust the verbosity level using the mip.display parameter: 

# where c is a Cplex object
c.parameters.mip.display.set(0)

See here for more info.

Tyler MacDonell
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  • thanks, but it doesn't work actually, I see the link, it is to block the message for mixed integer problems, I tried to find the one for linear programming problems, but failed. It seems cplex.setout(null) will work for C++ and Java, but no such command for python....sad about it – ilovecp3 Dec 04 '13 at 03:56
-1

Try this:

 ans = prob.solution.get_objective_value()
 print ans.split('\n')[-1]

Since Cplex is commercial I can't test if my solution is working. But you get the idea: split the string, get only what you want.

oz123
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  • Actually I am running a loop to solve an LP each iteration, I do can split the solution, but every time I need to scroll down A LOT to see the results even I split it. Thanks any way. – ilovecp3 Dec 04 '13 at 04:00
  • what do you mean you need to scroll down? where is the output going out to? to your teminal? when is it outputing? – oz123 Dec 04 '13 at 04:05