Adaptive grid segmentation error

[goord]

After many events, the parni grids tend to cause segmentation faults, most likely due to rounding errors after many iterations; create a program reproducing this issue (in a tractable amount of time) and fix the bug.

[Paraseus]

I managed to make the segfault reproducible within a few events for a SM mu-,nu_mubar > e-,nu_ebar process at 14 TeV. It happens exactly at the same point each time (because I use the same random seed). I did a valgrind trace, but it does not seem to like being copied here (due to parsing messing it up).