[Help-glpk] solve, add rows, resolve

[Brady Hunsaker]

Andrew,

I had previously thought that it was possible to do the following:

- create an LP instance
- solve with lpx_simplex()
- add rows with lpx_add_rows() and related functions
- re-solve starting from the same basis with lpx_simplex()  with 
LPX_K_DUAL set

However, this doesn't work for me.  This issue arose in testing the 
COIN-OR OSI interface, which expects that this is possible.

In fact, lpx_simplex may even abort without solving on the second 
attempt (it realizes that it's not a "fresh" problem, but the basis 
isn't there, or something like that).

Here are my questions:

- What behavior do you currently expect if rows are added and then 
lpx_simplex is solved?  (Solve again from existing basis, solve again as 
if it were a new instance, something else)

- Would you be interested in a patch that allows re-solving from the 
existing basis if possible?  (I might be able to write such a patch.)

- Do you want me to create a small test case to demonstrate the issue?

Thanks,
Brady

--
Brady Hunsaker
Assistant Professor
Industrial Engineering
University of Pittsburgh
http://www.engr.pitt.edu/hunsaker/