I have a small problem and I want have the dual solution.
 
But I find that the GLPK and LP-solve give me 2 different dual solution (the 
primal solution and the objective value is the same).
 
Could someone help to explain the reason?? 
( I give the mps file. )
 
Thanks
 
GLPK: 
Problem:    
   No.   Row name   St   Activity     Lower bound   Upper bound    Marginal
------ ------------ -- ------------- ------------- ------------- -------------
     1 R0           B        2071..61                             
     2 R1           NS           100           100             =       5.12392
     3 R2           NS           150           150             =       6.80022
     4 R3           NS           200           200             =       7.35016
     5 R4           NS           130           130             =      -4.45249
     6 R5           B            180           180             = 
     7 R6           NS           140           140             =      -2.51445
   No. Column name  St   Activity     Lower bound   Upper bound    Marginal
------ ------------ -- ------------- ------------- ------------- -------------
     1 x1           B            100             0               
     2 x2           NL             0             0                    0.576412
     3 x3           NL             0             0                     6.39053
     4 x4           B             30             0               
     5 x5           B            120             0               
     6 x6           NL             0             0                     1.93804
     7 x7           NL             0             0                     0.28821
     8 x8           B             60             0               
     9 x9           B            140             0               
 
LP-solve : 
Primal variables:
  Column name                      Value       Slack         Min         Max
  --------------------------------------------------------------------------
  x1                                 100           0     -1e+030      1e+030
  x2                                   0    0.576412         -30         100
  x3                                   0     6.39053         -30         100
  x4                                  30           0     -1e+030      1e+030
  x5                                 120           0     -1e+030      1e+030
  x6                                   0     1.93804         -60         120
  x7                                   0     0.28821        -120          30
  x8                                  60           0     -1e+030      1e+030
  x9                                 140           0     -1e+030      1e+030
Dual variables:
  Row name                         Value       Slack         Min         Max
  --------------------------------------------------------------------------
  R1                            0.671428         100         100         100
  R2                             2.34773         150         150         150
  R3                             2.89767         200         200         200
  R4                                   0         130     -1e+030      1e+030
  R5                             4.45249         180         180         180
  R6                             1.93804         140         140         140
 


      
*<meta creator='lp_solve v5.5'>
*<meta rows=6>
*<meta columns=9>
*<meta equalities=6>
*<meta integers=0>
*<meta origsense='MIN'>
*
NAME                  
ROWS
 N  R0      
 E  R1      
 E  R2      
 E  R3      
 E  R4      
 E  R5      
 E  R6      
COLUMNS
    x1        R0        0.6714280000   R1        1.0000000000
    x1        R4        1.0000000000
    x2        R0        5.7003300000   R1        1.0000000000
    x2        R5        1.0000000000
    x3        R0        9.0000000000   R1        1.0000000000
    x3        R6        1.0000000000
    x4        R0        2.3477300000   R2        1.0000000000
    x4        R4        1.0000000000
    x5        R0        6.8002200000   R2        1.0000000000
    x5        R5        1.0000000000
    x6        R0        6.2238100000   R2        1.0000000000
    x6        R6        1.0000000000
    x7        R0        3.1858800000   R3        1.0000000000
    x7        R4        1.0000000000
    x8        R0        7.3501600000   R3        1.0000000000
    x8        R5        1.0000000000
    x9        R0        4.8357100000   R3        1.0000000000
    x9        R6        1.0000000000
RHS
    RHS       R1        100.00000000   R2        150.00000000
    RHS       R3        200.00000000   R4        130.00000000
    RHS       R5        180.00000000   R6        140.00000000
ENDATA
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