we need to cap the timestep that VODE tries

[zingale]

VODE seems to want to try a timestep 3 or more orders of magnitude larger than the tmax we want to burn with. For simplified-SDC, this means that the advective term essentially evacuates a cell, leaving the density negative (or small_dens), which causes thermodynamic problems down the road.

We should cap the timestep at tmax / 2 or so. @jmsexton03 knows a bit about this.

This will help with:
AMReX-Astro/Castro#1596

[zingale]

oh, so it looks like we actually want what was itask = 4 in the original VODE (which we've since ripped out):

C          4  means normal computation of output values of y(t) at                                                                                                                              
 429 C             t = TOUT but without overshooting t = TCRIT.                                                                                                                                      
 430 C             TCRIT must be input as RWORK(1).  TCRIT may be equal to                                                                                                                           
 431 C             or beyond TOUT, but not behind it in the direction of                                                                                                                             
 432 C             integration.  This option is useful if the problem                                                                                                                                
 433 C             has a singularity at or beyond t = TCRIT.                               

[zingale]

turns out the issue was due to #643

It might be interesting to explore this in the future, but it is no longer critical