加快CPLEX C ++代码的速度

Question

This is the result of implementing my very first model in CPLEX C++ and I am very much surprised how slow and poor the quality is. I belief that much of it can be avoided by a better formulation. Can anyone help me improve the code, please? Hints, ideas, thoughts ... everything is appreciated!

It is about scheduling exams within 5 days that have 2 timeslots each available. My input is the number of exams (first row first number) and conflicting exam pairs (first row second number) where I also know the number of students taking both exams(in the following rows -> exam1 exam2 #students taking both exams). The code you can find here and the instance here .

The constraints I am including are:

1. each exams is scheduled exactly once
2. conflicting exams cannot be scheduled at the very same period
3. penalize if conflicting exams are scheduled on same day
4. penalize if conflicting exams are scheduled on consecutive days
5. penalize if conflicting exams are scheduled on adjacent periods over night

I have the feeling that something is even wrong in the formulation because I cannot imagine that the value of the objective value is that high. Does anyone see the flaw? I'm stuck.

The problem might be in the loop where I try to figure out whether a soft constraint is violated or not. There I am looping over days but probably I accidentally overwrite my variables all the time. Does anyone have an idea how to determine the binary variable indicating if the soft constraint is violated on any day (and of course it can happen only once but most probably it is not at the end).

Answer 1

Rather than debugging C++ code I just re-implemented the model using a modeling language (I believe that is quicker and a more pleasant way to spend a sunday evening).

(Note: updated after fixing bug). Here is my solution with a total penalty of 751:

You should be able to plug this into your code and verify the results.

Note: it took about 900 seconds on an old laptop to prove optimality with Cplex. If you want just a good solution, you can stop a little bit earlier:

(Blue line is the objective and the red line is the best possible bound). To get good performance I helped Cplex a little bit with setting branching priorities and using some options suggested by a tuning run.