[Cbc] some issues with LP file format

[fmargot at andrew.cmu.edu]

Hi Aditha:

> Folks,
> We are using v 2.7.5 of the cbc.exe and passing it a .lp file to help
> solve the model.
>
> While using this we identified few things to be careful of
> 1.      Using < or > in an equation in subject to leads to a crash. Using
> <= or >= works.
> a.      i.e. A + B < 10 will not work
> b.      A + B <= 10 will work
> 2.      When creating a constraint the format constraintName:
> constraintEquation the tool expects there to be no space between the
> constraint Name and the :
> a.      i.e. const1: A + B <=10 will work
> b.      const1 : A + B <= 10 will not work
> 3.      If the objective has two entries for the same variable then the
> last coefficient is used instead of
> a.      i.e. in objective if I have 10 A - 3 A then only -3 A will be
> considered
>
> we have modified our model generation to handle all these.
>
> Question:
> Are there other such know special handling that we need to be aware of
> while generating a .LP file?

You can look at the doxygen documentation for additional format
constraints.  See

http://www.coin-or.org/Doxygen/CoinUtils/classCoinLpIO.html

Point 1 should not be a surprise as strict inequalities are not part of a
usual LP model. Point 2 is listed in the doc. Point 3 is not listed and
should indeed be added to the doc (or fixed).

Francois