Exercise using Eplex
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A company produces two types of refrigerators T1 and T2, which
require the following resources to produce each unit of the product:

		Product	T1	T2
Resource
Labour (hours)		 9	 6
Pumps (units)		 1	 1
Tubing (m)		12	23

The amount of profit per unit of products are:

T1	350
T2	300

They have the following resources available:
1566 hours of labour, 200 pumps, and 2880 metres of tubing.



Tasks
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1. Write a program to maximise the profit for the company, using eplex as
    a black box solver.  Write a predicate that returns the profit and the
    values for T1 and T2.

2. What program change is required to answer this question:
    What profit can be achieved if exactly 150 units of T1 are required?

3. What would the profit be if fractional numbers of refrigerators could
    be produced?

4. Rewrite the program from (1) without optimize/2, using
    eplex_solver_setup/1, eplex_solve/1, and eplex_var_get/3.

5. In the program from (4), remove the integrality constraints (so that eplex
    only sees an LP problem).  Solve the integer problem by interleaving
    solving of the LP problem with a rounding heuristic:

    - solve the continuous relaxation
    - round the solution for T1 to the nearest integer and instantiate it
    - re-solve the new continuous relaxation
    - round the solution for T2 to the nearest integer and instantiate it
    - re-solve the new continuous relaxation

    What is the result in terms of T1, T2 and Profit?
 
6. Rewrite the program from (5) using eplex_solver_setup/4 and automatic
    triggering of the solver instead of explicit calls to eplex_solve/1.
    The solver should be triggered whenever variables get instantiated.