[petsc-users] PetscSortRealWithPermutation causes segfaults

[S V N Vishwanathan]

> This issue of hitting worst case of quicksort came up before with
> PetscSortInt. It would be interesting to know if the pivot selection
> in PetscSortInt_Private would fix the worst-case behavior that you
> see? If so, then the same changes could be made to the other sorting
> routines.

I did a bit more investigation and found that this worst case is
happening when all the elements of the array are the same. I am
detecting this in my code and avoid calling the sort as a stop gap
measure. 

I don't think there will be trouble with a O(n) memory in a queue but a
recursive call overflows the stack.

vishy