[Osi] CPLEX Error 1217: No solution exists

[Laszlo Ladanyi]

On Mon, 2 Jun 2008, Matthew Saltzman wrote:

>
> On Mon, 2008-06-02 at 18:00 -0400, Laszlo Ladanyi wrote:
>> No bug.
>>
>> Pure and implemented means that if a derived class does not implement it then
>> you get a compile time error. So it forces the user to think and implement
>> something for the method. However, there is a default implementation, so the
>> user can simply invoke the default implementation.
>
> OK But the "user" in this case is OsiCpx, right?

Yes.

> So what's the right
> behavior for OsiCpx?  Implement a method that just invokes the
> base-class method?
>

If that's the right (and fastest/simplest :-) thing to do, then yes.

The default getObjValue() implementation actually recomputes the objective 
value (multiplies the solution vector with the coeff vector and subtracts the 
offset). If that's what OsiCpx wants to do, because, e.g., cplex can't 
return the solution value because of problem change, but colsol is still 
cached, then do it. On the other hand the maintainer of OsiCpx may decide to 
do what cplex does and not return a sol value if things changed (which seems 
to be the current behavior). That approach can be justified, too.

That's why I was saying that making the method pure virtual forces the 
implemeter of the derived class to think a bit.

>>
>> --Laci
>>
>> On Mon, 2 Jun 2008, Matthew Galati wrote:
>>
>>> Umm... ok, header has pure (=0) but src has it implemented. Bug.
>>>
>>>> It looks to me like base implementation is pure virtual
>>>>     /// Get objective function value
>>>>     virtual double getObjValue() const = 0;
>>>>
>>>>
>>>>
>>>>> CPLEX wipes out all solution information as soon as you make any
>>>>> change to the problem whatsoever. I don't believe that the objective
>>>>> value is one of the things cached in the base class. If you look at
>>>>> the current implementation of getObjVal() in OsiCpx, it tries to get
>>>>> the objective value using CPXgetobjval(). If Cplex reports
>>>>> CPXERR_NO_SOLN, then the function returns 0.0 by default. In the base
>>>>> class, the default implementation of the getObjVal() function computes
>>>>> the objective value on the fly from cached data, which I guess would
>>>>> fix the problem. Try just commenting out the getObjVal() function in
>>>>> OsiCpx or else call the base class implementation from there and see
>>>>> if that does what you need.  If that works, we should probably make
>>>>> that change.
>>>>>
>>>>> Cheers,
>>>>>
>>>>> Ted
>>>>>
>>>>>
>>>>>
>>>>> Matthew Galati wrote:
>>>>>
>>>>>> This might be related to an old discussion...
>>>>>>
>>>>>> Using OsiCpx, I do
>>>>>>   initialSolve()
>>>>>>   getObjValue()
>>>>>>   addCols()
>>>>>>   getObjValue()  --> returns CPLEX Error  1217: No solution exists
>>>>>>
>>>>>> This is just an LP. Earlier issues with caching seem to have to do
>>>>>> with switching from MIP to LP, etc.
>>>>>>
>>>>>> It looks like some attempt to keep cache was already made. Any ideas?
>>>>>> If needed, I can create a driver program to show this issue.
>>>>>>
>>>>>> int err = CPXaddcols(env_,
>>>>>> getLpPtr(OsiCpxSolverInterface::KEEPCACHED_ROW),
>>>>>>                       numcols, nz, const_cast<double*>(obj),
>>>>>>                       start, index, elem,
>>>>>>                       const_cast<double*>(collb),
>>>>>>                       const_cast<double*>(colub), NULL );
>>>>>>
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>>>>>>
>>>>>
>>>>
>>>>
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> --
>                Matthew Saltzman
>
> Clemson University Math Sciences
> mjs AT clemson DOT edu
> http://www.math.clemson.edu/~mjs
>