[Help-glpk] Simplex method infeasible, IP method feasible

[Nicolo' Giorgetti]

Dear All,

Using the API routines I set up the basic LP problem 

     min  c'x
     s.to Ax <= b
          lb <= x <= ub
          x real

where

c=[1 0 0]',
A=[ -1  1        1
     1  0        0
     0 -0.22252  0.97493
     0 -0.90097  0.43388
     0 -0.90097 -0.43388
     0  0.62349 -0.78183],
b=[  0
    68.855
    39.483
     5.2338
   -73.042
    76.044],

lb=[-1e6 -1e6 -1e6]',
ub=[ 1e6  1e6  1e6]',

This problem is infeasible. In fact I solved it with
the lpx_simplex() function and lpx_get_status() returns LPX_NOFEAS
(183). 
I have tried then to solve it with the interior point method, by means
of the lpx_interior() function, but the lpx_get_ips_stats()
returns LPX_T_OPT(151) that is an optimal solution has been found. 
How is it possible ? 


Thanks for any comment.

Regards,
Nicolo'.