Code review comment for lp:~nickpapior/siesta/4.1-naive-aux-cell

It seems that there are two types of "errors" that can appear:

1. A supercell is not big enough. This causes a crash in 'hsparse', and should be avoided at all costs.

2. The supercell for the new geometry is different (because of cell changes), and thus the DM cannot be reused safely. In this case we could just skip the reuse of the DM for this particular instance.
Hopefully the number of times that this happens is limited, as changes will tend to become smaller and smaller (?).

Now, I believe it is true that the "naive-aux-cell" algorithm gives a safe auxcell for a given unit cell, isn't it? Note that to be completely sure we can run *always* the tight graph algorithm, but I do not think it is necessary.

Then we can leave the code as it is, recomputing nsc at each geometry, but checking whether nscold /= nsc, and in that case forbid the reuse of the DM.