[Bug-glpk] [Fwd: infinite loop doing /* restart the search */ with Warning: numerical instability]

[Andrew Makhorin]

-------- Forwarded Message --------
From: Jan Kolar <address@hidden>
To: address@hidden
Subject: infinite loop doing /* restart the search */ with Warning:
numerical instability
Date: Fri, 04 Jan 2013 07:24:19 +0100


Hello,

I have forced (very recent) glpk into endless loop in _glp_spx_primal().

I think the problem is in glpk-4.47/src/glpspx01.c
2652                rigorous = 5;
2653                goto loop;

Somethink like the following would make more sense to me
              if (rigorous < 5) {
                     rigorous = 5;
                     goto loop;
             } else {
                     // I do not know.   Proceed as it is    or  return 
with an error ?
                     // In my application: relax the tolerances slightly 
and loop once(1) more.
             }

I appreciate any fast reply to this, thank you.


---

The data size is small (m = 20, n = 9, nnz = 87), the problem extremely 
difficult.
(In my application I iterate to ask glpk for which parameter the problem 
is solvable :-).)

The symptom is that glpk endlessly  prints  Warning: numerical 
instability (primal simplex,...

Also I would suggest if memory allocations are right, since in this loop,
probably libglpk crashed my Win7+cygwin computer (after it produced 1.4 
GB of  "Warning: numerical instability" of output. Note: 100G free disk 
space after.)

I can send program generating the input data, if it is necessary.
(starting_point_id  = 4-130-130-125-162-116-147-191-159-019- )


Jan Kolar