Attempting to remove a package complains about unmet dependencies

I had the same problem. This saved me (replace with your package version):

sudo dpkg -i --force-overwrite /var/cache/apt/archives/libcublas-dev_10.2.1.243-1_amd64.deb

And then:

sudo apt --fix-broken install

dpkg: error processing archive /var/cuda-repo-10-1-local-10.1.243-418.87.00/./libcublas-dev_10.2.1.243-1_amd64.deb (--unpack): trying to overwrite '/usr/lib/x86_64-linux-gnu/libcublas_static.a', which is also in package nvidia-cuda-dev 9.1.85-3ubuntu1 dpkg-deb: error: paste subprocess was killed by signal (Broken pipe)

2 Packages ,that have the same file

sudo mv usr/lib/x86_64-linux-gnu/libcublas_static.a usr/lib/x86_64-linux-gnu/libcublas_static.a.bak

Then

sudo dpkg --configure -a 

If this work, try to purge cuda again