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[Help-glpk] Re: Simplex method infeasible, IP method feasible
From: |
Andrew Makhorin |
Subject: |
[Help-glpk] Re: Simplex method infeasible, IP method feasible |
Date: |
Wed, 10 Sep 2003 10:36:53 +0400 |
>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 ?
Why infeasible? I tried your example with both simplex and interior.
Here are the results below.
------------------------------------------------------------------------
param m;
param n;
param A{1..m,1..n};
param b{1..m};
param c{1..n};
param lb{1..n};
param ub{1..n};
var x{j in 1..n} >= lb[j] <= ub[j];
minimize Z: sum{j in 1..n} c[j] * x[j];
s.t. row{i in 1..m}: sum{j in 1..n} A[i,j] * x[j] <= b[i];
data;
param m := 6;
param n := 3;
param c := 1 1, 2 0, 3 0;
param A : 1 2 3 :=
1 -1 1 1
2 1 0 0
3 0 -0.22252 0.97493
4 0 -0.90097 0.43388
5 0 -0.90097 -0.43388
6 0 0.62349 -0.78183 ;
param b :=
1 0
2 68.855
3 39.483
4 5.2338
5 -73.042
6 76.044 ;
param lb default -1e6;
param ub default 1e6;
end;
------------------------------------------------------------------------
38 lines were read
Generating Z...
Generating row...
Model has been successfully generated
lpx_simplex: original LP has 7 rows, 3 columns, 13 non-zeros
lpx_simplex: presolved LP has 5 rows, 3 columns, 11 non-zeros
gm_scal: max / min = 4.494e+00
gm_scal: max / min = 3.016e+00
lpx_adv_basis: size of triangular part = 5
0: objval = -2.000000000e+06 infeas = 1.000000000e+00 (0)
4: objval = 6.885450326e+01 infeas = 0.000000000e+00 (0)
OPTIMAL SOLUTION FOUND
------------------------------------------------------------------------
Status: OPTIMAL
Objective: Z = 68.85450326 (MINimum)
Row name St Activity Lower bound Upper bound Marginal
------------ -- ------------- ------------- ------------- -------------
Z B 68.8545
row[1] NU 0 0 -1
row[2] B 68.8545 68.855
row[3] B -43.5373 39.483
row[4] B -93.4892 5.2338
row[5] NU -73.042 -73.042 -1.44146
row[6] NU 76.044 76.044 -0.479103
Column name St Activity Lower bound Upper bound Marginal
------------ -- ------------- ------------- ------------- -------------
x[1] B 68.8545 -1e+06 1e+06
x[2] B 92.4178 -1e+06 1e+06
x[3] B -23.5632 -1e+06 1e+06
------------------------------------------------------------------------
38 lines were read
Generating Z...
Generating row...
Model has been successfully generated
lpx_interior: original LP problem has 7 rows and 3 columns
lpx_interior: transformed LP problem has 9 rows and 12 columns
Factorizing S = A*A' symbolically...
nz(A) = 24
nz(S) = 32 (upper triangular part)
nz(U) = 32
Guessing initial point...
Optimization begins...
0: F = 2.522900541e+05; rpi = 3.0e-01; rdi = 1.1e+00; gap = 2.0e-01
1: F = -4.073511216e+04; rpi = 9.2e-02; rdi = 1.1e-01; gap = 1.8e-01
2: F = -1.149989554e+03; rpi = 1.1e-02; rdi = 1.3e-02; gap = 2.4e-02
3: F = -4.535554945e+01; rpi = 1.1e-03; rdi = 1.3e-03; gap = 2.5e-03
4: F = 6.094577995e+01; rpi = 1.2e-04; rdi = 1.3e-04; gap = 3.2e-04
5: F = 7.301120469e+01; rpi = 1.5e-05; rdi = 1.3e-05; gap = 5.8e-05
6: F = 7.071345903e+01; rpi = 2.3e-06; rdi = 1.7e-06; gap = 7.9e-06
7: F = 6.904303590e+01; rpi = 2.3e-07; rdi = 1.7e-07; gap = 8.1e-07
8: F = 6.887344654e+01; rpi = 2.3e-08; rdi = 1.7e-08; gap = 8.1e-08
9: F = 6.885634138e+01; rpi = 2.3e-09; rdi = 1.7e-09; gap = 8.1e-09
OPTIMAL SOLUTION FOUND
------------------------------------------------------------------------
Status: INTERIOR OPTIMAL
Objective: Z = 68.85634138 (MINimum)
Row name Activity Lower bound Upper bound Marginal
------------ ------------- ------------- ------------- -------------
Z 68.8563 0
row[1] 0.0024996 0 -1.09566
row[2] 68.8563 68.855 -0.0956563
row[3] -43.5318 39.483 -1.40115e-05
row[4] -93.4859 5.2338 -1.68234e-05
row[5] -73.0434 -73.042 -1.57935
row[6] 76.0391 76.044 -0.52496
Column name Activity Lower bound Upper bound Marginal
------------ ------------- ------------- ------------- -------------
x[1] 68.8563 -1e+06 1e+06 0
x[2] 92.4166 -1e+06 1e+06 0
x[3] -23.5578 -1e+06 1e+06 0
- [Help-glpk] Simplex method infeasible, IP method feasible, Nicolo' Giorgetti, 2003/09/09
- [Help-glpk] Re: Simplex method infeasible, IP method feasible,
Andrew Makhorin <=
- Re: [Help-glpk] Re: Simplex method infeasible, IP method feasible, Nicolo' Giorgetti, 2003/09/11
- [Help-glpk] Re: Simplex method infeasible, IP method feasible, Andrew Makhorin, 2003/09/11
- Re: [Help-glpk] Re: Simplex method infeasible, IP method feasible, Nicolo' Giorgetti, 2003/09/12
- [Help-glpk] Re: Simplex method infeasible, IP method feasible, Andrew Makhorin, 2003/09/12
- [Help-glpk] Re: Simplex method infeasible, IP method feasible, Nicolo' Giorgetti, 2003/09/12
- [Help-glpk] Re: Simplex method infeasible, IP method feasible, Andrew Makhorin, 2003/09/12
- Re: [Help-glpk] Re: Simplex method infeasible, IP method feasible, Nicolo' Giorgetti, 2003/09/13
- [Help-glpk] Re: Simplex method infeasible, IP method feasible, Andrew Makhorin, 2003/09/11