If I’m right and I don’t need to install cuda and cudnn on my system so long as I have cudatools installed in Anaconda (could someone confirm this?), then the most likely source of my problem may be the nvidia driver, which is designed for CUDA 10.2 while PyTorch uses 10.1.  I fell back to nvidia-driver-435.  nvidia-smi now shows CUDA version as 10.1 and so far I haven’t run into any errors in PyTorch.  Fingers crossed.