Incorrect MPS import

[drdv]

Details for the issue

Consider the MPS file (taken from here)

NAME          TESTPROB
ROWS
 N  COST
 L  LIM1
 G  LIM2
 E  MYEQN
COLUMNS
    XONE      COST                 1   LIM1                 1
    XONE      LIM2                 1
    YTWO      COST                 4   LIM1                 1
    YTWO      MYEQN               -1
    ZTHREE    COST                 9   LIM2                 1
    ZTHREE    MYEQN                1
RHS
    RHS1      LIM1                 5   LIM2                10
    RHS1      MYEQN                7
BOUNDS
 UP BND1      XONE                 4
 LO BND1      YTWO                -1
 UP BND1      YTWO                 1
ENDATA

What did you do?

Executed _, problem = pulp.LpProblem.fromMPS('test.mps')

What did you expect to see?

I expected for the LIM2 constraint to be LIM2: XONE + ZTHREE >= 10

What did you see instead?

TESTPROB:
MINIMIZE
1.0*XONE + 4.0*YTWO + 9.0*ZTHREE + 0
SUBJECT TO
LIM1: XONE + YTWO <= 5

LIM2: XONE + ZTHREE >= 0

MYEQN: - YTWO + ZTHREE = 7

VARIABLES
XONE <= 4 Continuous
-1 <= YTWO <= 1 Continuous
ZTHREE Continuous

In my test, all MPS files whose RHS section contains definitions in Fields 5 & 6 are not imported correctly. The following modification of the MPS file is imported correctly (I simply manually moved the LIM2 RHS specification):

NAME          TESTPROB
ROWS
 N  COST
 L  LIM1
 G  LIM2
 E  MYEQN
COLUMNS
    XONE      COST                 1   LIM1                 1
    XONE      LIM2                 1
    YTWO      COST                 4   LIM1                 1
    YTWO      MYEQN               -1
    ZTHREE    COST                 9   LIM2                 1
    ZTHREE    MYEQN                1
RHS
    RHS1      LIM1                 5
    RHS1      LIM2                10
    RHS1      MYEQN                7
BOUNDS
 UP BND1      XONE                 4
 LO BND1      YTWO                -1
 UP BND1      YTWO                 1
ENDATA

I tested with pysmps and it imports both versions of the MPS file correctly.

Useful extra information

What operating system are you using?

Linux: (Fedora)

I'm using python version:

3.10.2

I installed PuLP via:

• pypi (python -m pip install pulp)
• github (python -m pip install -U git+https://github.com/coin-or/pulp)

Did you also

• Tried out the latest github version: https://github.com/coin-or/pulp
• Searched for an existing similar issue: https://github.com/coin-or/pulp/issues?utf8=%E2%9C%93&q=is%3Aissue%20

It seems related to #459