Re: [Help-glpk] GLPK just hangs

[Xypron]

Hello Manish,

>> The weirdness is not that it just gets stuck in an infinite loop. 
The weird
>> part is that it works fine if instead of calling 
lpx_simplex/lpx_integer on
>> the problem that is already in memory, I write the problem to a file 
and load it again.

When writing a problem to file and loading it again some rounding will 
occur.

>> Also, can anyone explain to me the meaning of various lines of GLPK 
output, e.g.:
>> + 49135: mip = -5.000000000e-001 <= -2.500000000e-001 50.0% (46; 6967)

Read subsection "Terminal output" in section "2.9.5 glp intopt—solve MIP 
problem with the branch-and-cut method" of doc/glpk.pdf.

Though this is not the cause of your problem lpx_simplex is not part of 
the documented API.
Consider updating your program to the functions documented in doc/glpk.pdf.

Best regards

Xypron



Manish Jain wrote:
> Hello all,
>
> I have a cut/column generation implementation using GLPK 4.44 in Java.
> I am seeing some weird behavior when I increase the problem size.
> Glpk just gets stuck in an infinite loop every time after 42 iterations in my 
> case. The problem size is big here (details in the attachment).
>
> The weirdness is not that it just gets stuck in an infinite loop. The weird 
> part is that it works fine if instead of calling lpx_simplex/lpx_integer on the 
> problem that is already in memory, I write the problem to a file and load it 
> again.
> i.e.
> lpx_simplex(lp);
> lpx_integer(lp)<- Glpk gets stuck. There is no discernible error message. 
> Output log attached.
>
> lpx_write_cpxlp(lp, fileName)
> lpx_delete_prob(lp)
> lp = lpx_create_prob()
> lp = lpx_read_cpxlp(fileName)
> lpx_simple(lp);
> lpx_integer(lp);<- Works and gives the solution in about 2 seconds
>
> Additionally, if I write the problem to a file when it gets stuck, then I can 
> solve it with glpsol --lp fileName in a matter of 2 secs without any troubles 
> as well.
>
> Any ideas, anyone?
> Also, can anyone explain to me the meaning of various lines of GLPK output, 
> e.g.:
> + 49135: mip = -5.000000000e-001<= -2.500000000e-001  50.0% (46; 6967)
> Are these: [Iteration No] [Problem Class] [... ?] ( ...; row-No)
>
> I am using GLPK-4.44 Java bindings.
> The code is all in Java.
> Output log is attached.
>
> Thanks.
>
> Manish Jain
> University of Southern California
>   
>
>
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