View the model
Download the model

 Two level blending or pooling model(POOLING_PQ).
   Raw materials are selectively blended into pools, e.g., storage tanks,
   then pools are blended into finished products.
    We want to maximize the profit = sales of finished goods,
   minus cost of raw materials purchased,
    subject to satisfying quality requirements,
   such as density, sulfur fraction, Octane Number etc.
     This formulation uses the PQ formulation.
  It can also be thought of as a path formulation, in which we
 introduce variables to represent all possible paths of flow through
 the network. This formulation is much better w.r.t. finding a 
 globally optimal solution quickly. 
    
! Refs: Dey, S. and A. Gupte (2015), "Analysis of MILP Techniques for the Pooling Problem ,"
    Operations Research, vol. 63, No. 2, pp. 412–427.;
! Audet, C,  J. Brimberg, P. Hansen, S. Le Digabel, N. Mladenović (2004)
    "Pooling Problem: Alternate Formulations and Solution Methods," Management Science
    vol. 50, no. 6, pp 709-853.;
! Haverly, C. A. (1978), “Studies of the Behavior of Recursion for the Pooling Problem”,
   SIGMAP Bulletin, Association for Computing Machinery, no. 25 (Dec.);