Linear Programming - loading LP or MPS file?

[Craig E Larson]

I see that there are methods for saving a LP as and LP or MPS file in Sage. Is it possible to *load* an LP from one of these file types? The online help that I've found doesn't mention this or give examples of how to do it.

Thanks!

Craig

[Dima Pasechnik]

On Tuesday, 1 September 2015 07:00:39 UTC-7, Craig E Larson wrote:

I see that there are methods for saving a LP as and LP or MPS file in Sage. Is it possible to *load* an LP from one of these file types? The online help that I've found doesn't mention this or give examples of how to do it.

Not that I know. Write one, it will be a valuable addition to Sage...
(There should be Python code out there on the next that can be adapted, surely...)

Dima

Thanks!

Craig

[Stephen Hartke]

> On Tuesday, 1 September 2015 07:00:39 UTC-7, Craig E Larson wrote:
>> I see that there are methods for saving a LP as and LP or MPS file in
>> Sage. Is it possible to *load* an LP from one of these file types? The
>> online help that I've found doesn't mention this or give examples of how to
>> do it.

On Tue, Sep 1, 2015 at 10:49 AM, Dima Pasechnik <dim...@gmail.com> wrote:
> Not that I know. Write one, it will be a valuable addition to Sage...
> (There should be Python code out there on the next that can be adapted, surely...)

Most (all?) of the LP/IP libraries have functions for reading in LP
and MPS files, so it might be simpler to make Python wrappers around
that function in each of the backends.

Best wishes,
Stephen

[Dima Pasechnik]

How would it solve the issue of communicating with the frontend?
 

Best wishes,
Stephen

[Nathann Cohen]

> How would it solve the issue of communicating with the frontend?

For this I expect that we should be able to write a function
LP_from_file that returns both a MixedIntegerLinearProgram object and
a MIPVariable object, and that we will have to hack the MIPVariable
object a bit so that it matches the right variables in the MILP
object. Should not be much more involved than just force the integer
ID associated with a label.

Nathann

[Dima Pasechnik]

isn't it a bit too much code to have this for each backend, rather than just something that communicates with the
frontend only?

 

Nathann

[Nathann Cohen]

> isn't it a bit too much code to have this for each backend, rather than just
> something that communicates with the
> frontend only?

Indeed. Were you thinking of something like that?

1) Use GLPK to load a LP/MPS from a file
2) Read the MILP at Python-level
3) Use the info to create a new MILP object, and return it along with
the MIPVariable

Nathann

[Dima Pasechnik]

It seems that 3) should disregard MIPVariable. Otherwise, how do you use a
backend different from GLPK?

I think something like "from_file=..." argument in MixedIntegerLinearProgram() should be implemented,
and it ought to be compatible with "solver=...".
Behind the curtains it can talk to GLPK, no problem...

Dima

Nathann