It looks like I have found part of my confusion.
I have now reinstalled firedrake with PETSC_DIR unset, so there is an old PETSc (i.e. 3.4.2) inside the firedrake directory. But if I run activate later it seems to use the value of PETSC_DIR at that time.
This is my working explanation for why I get seg faults and why "gdb --args python3 MYSCRIPT.py" shows backtraces with the wrong PETSc (i.e. the 3.9 version I am using for other purposes).
So it looks like I should do
$ unset PETSC_DIR
$ source firedrake/bin/activate
every time I start firedrake? Is this the correct action if one has PETSC_DIR set?
Ed
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Ed Bueler
Dept of Math and Stat and Geophysical Institute
University of Alaska Fairbanks
Fairbanks, AK 99775-6660
301C Chapman