No feasible mixed integer solution

Presolves can cause unusual behavior when there is no feasible integer solution.  A mixed integer programming problem (presol2.gms) was tried which did not have a feasible integer solution.

variables z;

integer variables y1,y2;

equations r1,r2,r3,r4;

   r1..  z=e=y1+y2;

   r2..  y1=g=0.10;

   r3..  y2=g=0.10;

   r4..  y1+y2=l=1;

model badpresol /all/

option mip=cplex;

solve badpresol using mip maximizing z;

Solving this problem with CPLEX yielded the solution messages

**** SOLVER STATUS     1 NORMAL COMPLETION

**** MODEL STATUS      10 INTEGER INFEASIBLE

followed by

Presolve found MIP to be infeasible or unbounded.

Switching to RMIP in hopes LP solution will help with diagnosis.

Problem is integer infeasible

and no solution report.  XA, XPRESS and BDMLP all terminate in a similar fashion although some do return a solution report.

The OSL presolve did not discover problems and cratered.

Presolve...

 Crashing...

 Primal Simplex...

    Iter             Objective   Sum Infeasibilities

 **** Severe problem in OSL. Check the listing file.

      Terminating...

--- Restarting execution

--- PRESOL2.GMS(14) 0 Mb

--- Reading solution for model badpresol

--- PRESOL2.GMS(14) 0 Mb 1 Error

*** Status: Execution error(s)

In these cases, one needs to investigate the LST file to find the messages from the presolve processor to see what happened.  Also one may need to suppress the presolve using a solver options file.