unable to upgrade from ubuntu 16.04 to 18.04

[Mike]

after running: sudo do-release-upgrade -d -m desktop
Checking for a new Ubuntu release
Get:1 Upgrade tool signature [819 B]
Get:2 Upgrade tool [1,258 kB]
Fetched 1,259 kB in 0s (0 B/s)
authenticate 'bionic.tar.gz' against 'bionic.tar.gz.gpg'
extracting 'bionic.tar.gz'

Reading cache

Checking package manager
Reading package lists... Done
Building dependency tree
Reading state information... Done
Get:1 file:/var/cuda-repo-9-1-local-compiler-update-1 InRelease
Ign file:/var/cuda-repo-9-1-local-compiler-update-1 InRelease
Get:2 file:/var/cuda-repo-9-1-local-cublas-performance-update-1 InRelease
Ign file:/var/cuda-repo-9-1-local-cublas-performance-update-1 InRelease
Get:3 file:/var/cuda-repo-9-1-local-cublas-performance-update-3 InRelease
Ign file:/var/cuda-repo-9-1-local-cublas-performance-update-3 InRelease
Get:4 file:/var/cuda-repo-9-1-local InRelease
Ign file:/var/cuda-repo-9-1-local InRelease
Get:5 file:/var/cuda-repo-9-1-local-compiler-update-1 Release [574 B]
Get:6 file:/var/cuda-repo-9-1-local-cublas-performance-update-1 Release [574 B]
Get:7 file:/var/cuda-repo-9-1-local-cublas-performance-update-3 Release [574 B]
Get:8 file:/var/cuda-repo-9-1-local Release [574 B]
Get:9 file:/var/cuda-repo-9-1-local-compiler-update-1 Release [574 B]
Get:10 file:/var/cuda-repo-9-1-local-cublas-performance-update-1 Release [574 B]
Get:11 file:/var/cuda-repo-9-1-local-cublas-performance-update-3 Release [574 B]
Get:12 file:/var/cuda-repo-9-1-local Release [574 B]
Hit http://us.archive.ubuntu.com/ubuntu xenial InRelease
Get:13 http://us.archive.ubuntu.com/ubuntu xenial-updates InRelease [109 kB]
Get:14 http://security.ubuntu.com/ubuntu xenial-security InRelease [107 kB]
Hit http://ppa.launchpad.net/ubuntu-toolchain-r/test/ubuntu xenial InRelease
Hit https://packages.microsoft.com/ubuntu/16.04/prod xenial InRelease
Hit https://packages.microsoft.com/repos/vscode stable InRelease
Get:15 https://desktop-download.mendeley.com/download/apt stable InRelease [2,456 B]
Fetched 218 kB in 0s (0 B/s)
Reading package lists... Done
Building dependency tree
Reading state information... Done

Updating repository information

Third party sources disabled

Some third party entries in your sources.list were disabled. You can
re-enable them after the upgrade with the 'software-properties' tool
or your package manager.

To continue please press [ENTER]

Hit http://us.archive.ubuntu.com/ubuntu bionic InRelease
Hit http://us.archive.ubuntu.com/ubuntu bionic-updates InRelease
Hit http://security.ubuntu.com/ubuntu bionic-security InRelease
Fetched 0 B in 0s (0 B/s)

Checking package manager
Reading package lists... Done
Building dependency tree
Reading state information... Done

Calculating the changes

Calculating the changes

Could not calculate the upgrade

An unresolvable problem occurred while calculating the upgrade.

This can be caused by:
* Upgrading to a pre-release version of Ubuntu
* Running the current pre-release version of Ubuntu
* Unofficial software packages not provided by Ubuntu

If none of this applies, then please report this bug using the
command 'ubuntu-bug ubuntu-release-upgrader-core' in a terminal.

Restoring original system state

Aborting
Reading package lists... Done
Building dependency tree
Reading state information... Done

The upgrade fails

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: ubuntu-release-upgrader-core 1:16.04.25
ProcVersionSignature: Ubuntu 4.15.0-34.37~16.04.1-generic 4.15.18
Uname: Linux 4.15.0-34-generic x86_64
NonfreeKernelModules: sep4_1 socperf2_0 pax nvidia_modeset nvidia
ApportVersion: 2.20.1-0ubuntu2.18
Architecture: amd64
CrashDB: ubuntu
CurrentDesktop: Unity
Date: Tue Sep 18 14:10:45 2018
InstallationDate: Installed on 2018-05-02 (138 days ago)
InstallationMedia: Ubuntu 16.04.3 LTS "Xenial Xerus" - Release amd64 (20170801)
PackageArchitecture: all
SourcePackage: ubuntu-release-upgrader
UpgradeStatus: Upgraded to xenial on 2018-09-18 (0 days ago)

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Brian Murray (brian-murray)]

Thank you for taking the time to report this bug and helping to make Ubuntu better. The error that you are a reporting is a package conflict between a package from the official Ubuntu archive and a package from the ubuntu-toolchain-r test PPA. To resolve this situation please uninstall the packages from that PPA using the tool 'ppa-purge' which is provided by the ppa-purge package. Then try performing the distribution upgrade operations again. Thanks in advance!