$title Chemical Equilibrium Problem as MCP (WALLMCP,SEQ=127)

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A sample nonlinear system to solve chemical equilibrium models.

Wall, T W, Greening, D, and Woolsey, R E D, Solving Complex Chemical
Equilibria Using a Geometric-Programming Based Technique. OR 34, 3
(1987).

Keywords: mixed complementarity problem, chemical equilibrium model, chemical
          engineering
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Variable ba, so4, baoh, oh, hso4, h;

Equation r1, r2, r3, r4, b1, b2;

* Scaling in powers of 10: ba -5, so4 -5, baoh -12, oh -7, hso4 -10, h -7
r1.. ba*so4         =e= 1;
r2.. baoh/ba/oh     =e= 4.8;
r3.. hso4/so4/h     =e=  .98;
r4.. h*oh           =e= 1;
b1.. ba + 1e-7*baoh =e= so4 + 1e-5*hso4;
b2.. 2*ba + 1e-7*baoh + 1e-2*h =e= 2*so4 + 1e-5*hso4 + 1e-2*oh;

Model wall / all /;

ba.l   = 1;
so4.l  = 1;
baoh.l = 1;
oh.l   = 1;
hso4.l = 1;
h.l    = 1;

solve wall using mcp;