The reasons were essentially those already observed, but interestingly enough, the two tools did not (usually) fail on the same instances, meaning that a difficult instance for one tool might not be so difficult for the other.
PMS5 [ 7] computes the common d-neighbors of three l-mers using integer programming formulation, which is an efficient algorithm for solving the difficult instances of PMS: (21, 8) and (23, 9).
In colon cancer, we raise prediction accuracy in the most difficult instances from 87% to 93% for cancer versus non−cancer and from 83% to (astonishing) 92%, for with versus without liver metastasis, in well-established cross-platform evaluation schemes.
Using W4 (the smallest forbidden subgraph for monopolar graphs) as a cutting plane also helps little, solving one more instance, but might be useful for difficult instances with long running time.
It can be difficult, for instance, to dock the device with the recharger.
That makes it difficult, for instance, for women who need maternity leave.
It is very difficult, for instance, for my team to make appointments with Alex, a young homeless woman with a criminal record and without a mobile phone, who suffers horrific hallucinations of abuse.
Getting a divorce would be difficult, for instance, if the couple lived in or moved to a state that didn't recognize their union.
The distance from the stage diminished some of the duet's intimacy; it was difficult, for instance, to fully grasp the direction of the eyes, the rapid-fire lifting and lowering of the eyebrows and even the thrilling vibration of fluttering fingers.
It is difficult, for instance, to fathom how the speech given by one defendant could have constituted "co-operation with opponents of the regime" when it hardly strayed from her field of expertise, the environment.
