Restrict the time step variability

[ikorotkin]

The time steps $dt_{n} / dt_{n+1}$ can vary a lot. However, if the time step changes drastically (e.g., from 100.0 to 1e-8), this may lead to precision loss.

Solution:

• Add solver parameter - maximum $dt_{n} / dt_{n+1}$
• Roll the solution one step back and readjust the time step