Here's an update. (I posted the original question before looking at my notes.)
As root, I tried to free some memory with this command:
$ echo 1 > /proc/sys/vm/overcommit_memory
I then ran matlab from the command line and got these messages:
$ matlab
MATLAB is selecting SOFTWARE rendering.
MESA-LOADER: failed to open nouveau: /usr/lib/dri/nouveau_dri.so: cannot open shared object file: No such file or directory (search paths /usr/lib/x86_64-linux-gnu/dri:\$${ORIGIN}/dri:/usr/lib/dri, suffix _dri)
MESA-LOADER: failed to open kms_swrast: /usr/lib/dri/kms_swrast_dri.so: cannot open shared object file: No such file or directory (search paths /usr/lib/x86_64-linux-gnu/dri:\$${ORIGIN}/dri:/usr/lib/dri, suffix _dri)
MESA-LOADER: failed to open swrast: /usr/lib/dri/swrast_dri.so: cannot open shared object file: No such file or directory (search paths /usr/lib/x86_64-linux-gnu/dri:\$${ORIGIN}/dri:/usr/lib/dri, suffix _dri)
The MATLAB window then opened, but does not give me the prompt in the command window (10 minutes so far).