[Clp] Assertion `!diffUpper||fabs(diffLower-diffUpper)<1.0e-5' failed

[Lasse Kliemann]

I confirm it is completely fixed in revision 2183. Thanks!

John Forrest <john.forrest at fastercoin.com> writes:

> I managed to get the error.  Looking more closely the assert is stupid - 
> and also the code which led to the assert is probably not very reliable.
>
> I have modified ClpSolve.cpp.  However to duplicate your bug, I 
> downloaded the latest CoinAll and it is wildly out of date - January 
> this year - so I would use svn where possible.
>
> John Forrest
> On 27/10/15 19:52, Lasse Kliemann wrote:
>> Dear John, thanks for your help.
>>
>> Further tests revealed that the error happens with newer versions as
>> well (I tested up to CoinAll-1.7.5) -- but only if
>>
>>    -Xlinker -Rxxx
>>
>> is used for building the libraries, even if xxx points to an empty
>> directory. Without this directive, it is fine.
>>
>> So it looks more like a build problem, at least for newer versions.
>>
>> John Forrest <john.forrest at fastercoin.com> writes:
>>
>>> Lasse,
>>>
>>> I am unable to reproduce error using latest Osi stable 0.107.
>>>
>>> I compiled in stable 2.9/Cbc/examples so was using Clp 1.16 and
>>> Coinutils 2.10
>>>
>>> John Forrest
>>>
>>> On 27/10/15 15:04, Lasse Kliemann wrote:
>>>> The program below will give the error:
>>>>
>>>>     ClpSolve.cpp:1792: int ClpSimplex::initialSolve(ClpSolve&):
>>>>     Assertion `!diffUpper||fabs(diffLower-diffUpper)<1.0e-5' failed.
>>>>
>>>> when compiled against Osi 0.97.0 or newer, but is ok for 0.96.1 or
>>>> older.
>>>>
>>>> The LP has n^3 variables and 3*n constraints. The matrix has three
>>>> 1-entries in each column, distributed in a certain pattern. This LP is
>>>> feasible.
>>>>
>>>> The error goes away when n < 19 or when the upper row bound is set to
>>>> 1.0 (matching the lower bound) or larger than 2.0.
>>>>
>>>> Could anyone please provide some insight on this? The diff between
>>>> 0.96.1 and 0.97.0 probably holds the answer, but I'm not qualified to
>>>> analyze it. Thanks!
>>>>
>>>> #include <cstring>
>>>> #include <OsiClpSolverInterface.hpp>
>>>> #include <CoinModel.hpp>
>>>>
>>>> int main() {
>>>>     const double ones[3] = { 1, 1, 1 };
>>>>     const int n = 19;             // n < 19 eliminates error
>>>>     const double row_upper = 1.1; // 1.000001 <= row_upper <= 2.0 gives error
>>>>     CoinModel model;
>>>>     for(int i=0; i<n; ++i)
>>>>       for(int j=0; j<n; ++j)
>>>>         for(int k=0; k<n; ++k) {
>>>> 	int rows[3]; rows[0]=i; rows[1]=n+j; rows[2]=2*n+k;
>>>> 	model.addColumn(3, rows, ones, 0.0, 1.0, 1.0);
>>>>         }
>>>>     for(int i=0; i<3*n; ++i) model.setRowBounds(i, 1.0, row_upper);
>>>>     OsiClpSolverInterface si;
>>>>     si.loadFromCoinModel(model);
>>>>     si.initialSolve();
>>>> }
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