problem reading .lp files

[Fabian Hoermann]

Dear Colleagues,

i have problems with reading .lp-Files. Here is my error, after i typed m=read("inst2501.lp")

-------------------------------------------------------------------
Unable to read file
Traceback (most recent call last):
      File "<stdin>", line 1, in <module>
      File "gurobi.pxi", line 1997, in gurobipy.read (../../src/python/gurobipy.c:64310)
      File "gurobi.pxi", line 56, in gurobipy.gurobi.read (../../src/python/gurobipy.c:62689)
gurobipy.GurobiError: Unable to read model
------------------------------------------------------------------

The .lp File seems to be correct, as CPLEX can read it. Is there a better solution than converting the .lp-File to .mps ?

Sincerely yours

[T.]

There is no common standard for LP files, so it can happen that CPLEX can read files that Gurobi cannot read. For example, Gurobi needs spaces between numbers and operators, etc.

Could you post your LP file?

[Fabian Hoermann]

Hi,

thanks for your answer. Here is an example:

Maximize
 obj:  +132 x#1#2#3 +146 x#1#2#4 +163 x#1#2#5 +131 x#1#3#4 +56 x#1#3#5 +133 x#1#4#5
  +139 x#2#3#4 +159 x#2#3#5 +170 x#2#4#5 +122 x#3#4#5
Subject to
 feasibility_1:
  + x#1#4#5 + x#1#3#5 + x#1#3#4 + x#1#2#5 + x#1#2#4 + x#1#2#3
  <= 1
 feasibility_2:
  + x#1#2#5 + x#1#2#4 + x#1#2#3 + x#2#4#5 + x#2#3#5 + x#2#3#4
  <= 1
 feasibility_3:
  + x#1#2#3 + x#2#3#5 + x#2#3#4 + x#1#3#5 + x#1#3#4 + x#3#4#5
  <= 1
 feasibility_4:
  + x#2#3#4 + x#1#3#4 + x#1#2#4 + x#3#4#5 + x#2#4#5 + x#1#4#5
  <= 1
 feasibility_5:
  + x#3#4#5 + x#2#4#5 + x#2#3#5 + x#1#4#5 + x#1#3#5 + x#1#2#5
  <= 1

User Cuts
 upperBound_1U:
  + x#3#4#5 + x#2#4#5 + x#2#3#5 + x#2#3#4 + x#1#4#5 + x#1#3#5
  + x#1#3#4 + x#1#2#5 + x#1#2#4 + x#1#2#3 <= 1
Bounds
 0 <= x#1#2#3 <= 1
 0 <= x#1#2#4 <= 1
 0 <= x#1#2#5 <= 1
 0 <= x#1#3#4 <= 1
 0 <= x#1#3#5 <= 1
 0 <= x#1#4#5 <= 1
 0 <= x#2#3#4 <= 1
 0 <= x#2#3#5 <= 1
 0 <= x#2#4#5 <= 1
 0 <= x#3#4#5 <= 1
General
 x#1#2#3
 x#1#2#4
 x#1#2#5
 x#1#3#4
 x#1#3#5
 x#1#4#5
 x#2#3#4
 x#2#3#5
 x#2#4#5
 x#3#4#5
End

kind regards

[Greg Glockner]

> User Cuts
> upperBound_1U:
> + x#3#4#5 + x#2#4#5 + x#2#3#5 + x#2#3#4 + x#1#4#5 + x#1#3#5
> + x#1#3#4 + x#1#2#5 + x#1#2#4 + x#1#2#3 <= 1

This is proprietary to CPLEX. You will need to write this as a constraint or use the APIs to implement a cut.

[T.]

As a quick and dirty fix, it should be sufficient to remove the line "User Cuts" from the file.

[Fabian Hoermann]

Thanks to both of you for your answers.

Best regards

[Morgrim X]

I am having this problem now.  I can't find a reference guide that explains the lp format that Gurobi requires.  I'm not even sure how to make a comment

I have saved it as a text file d=format using the .lp extension in Windows 8.1's notepad.

The gurobi examples have no comment.  It looks like there is no CRLF.

I have no idea what I have to do. 

[Renan Garcia]

Have a look at http://www.gurobi.com/documentation/6.0/reference-manual/lp_format. For example, the backslash symbol '\' starts a comment.

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[Morgrim X]

Thank you so much.  Some of my variable names begin with a number.

I hope that's the problem. 

It would be nice if the parser gave a meaningful error message.

I presume any text file using the correct format would be readable.

[Morgrim X]

I failed to show the error I'm getting.  I think it's identical to the code the person who opened this thread had:

gurobi> m = read("C:\Users\Public\Towers.lp")

Unable to read file
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>

  File "gurobi.pxi", line 2002, in gurobipy.read (../../src/python/gurobipy.c:68
614)
  File "gurobi.pxi", line 57, in gurobipy.gurobi.read (../../src/python/gurobipy
.c:66993)

gurobipy.GurobiError: Unable to read model

gurobi>


Since then, I renamed the file, but this is the error I get  every time.

[Renan Garcia]

Are tokens "T1Def <96> 1500" supposed to be a single variable name? Spaces are not allowed in the LP format.

[Morgrim X]

I found some errors in my model, fixed them, and still get the same error messages:

gurobi> m = read("C:\Users\Micky Lee\Documents\Empire\Towers.lp")

Unable to read file
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "gurobi.pxi", line 2002, in gurobipy.read (../../src/python/gurobipy.c:68
614)
  File "gurobi.pxi", line 57, in gurobipy.gurobi.read (../../src/python/gurobipy
.c:66993)
gurobipy.GurobiError: Unable to read model
gurobi>

Attached is the file associated with these errors.  Everything seems so straightforward.  This is driving me nuts.

[Morgrim X]

I found my error.  I hope no one wasted too much time on this.

I had a number of entries where I included a multiplier symbol, *, e.g. 2 * X.  It should read 2 X.

Duh.

[Erwin Kalvelagen]

Try to replace \ with / in the path of your input file.

----------------------------------------------------------------
Erwin Kalvelagen
Amsterdam Optimization Modeling Group
er...@amsterdamoptimization.com
http://amsterdamoptimization.com
----------------------------------------------------------------

--

[Morgrim X]

Yes.  Thank you. I noticed that before and moved on.  I appreciate your help