Hi there PETSc, I am working my way through ex11.c and have encountered a problem. On the first pass through mesh adaption, the gradient computation in PETSc triggers a NaN, even though none of the input data are NaN. To reproduce: PETSc v3.15 with latest MPICH, no external libraries, debugging on Compile ex11.c using GCC 9.3 on Ubuntu 20.04 Run as: ./ex11 -ufv_use_amr -fp_trap Running under GDB shows that the offending line is: src/dm/impls/plex/plexfvm.c:111 This originates from the call to DMPlexReconstructGradientsFVM. I only noticed this because I was trying to resolve a discontinuity in my own initial condition for a Sod shock tube problem, but then I found that it occurs in the example without any modification, too. Is this somehow intended? If not, what steps can one take to make sure the gradients are actual numeric values? It doesn't make sense to me that they would be undefined on the first step when nothing else is NaN. Or is it that AMR in ex11 doesn't quite work yet? Thanks, Ellen Price