have spent days if not months installing CUDA 7.0 and CUDA 7.5 in Ubuntu 14.04 and Ubuntu 16.04 over different laptops(Dell and Asus). I finally got them working. While there are numerous tutorials present over the web, most are incomplete and error prone. The difficulty comes in installing the Nvidia drivers. If one does a mistake then the system crashes(since you need Nvidia drivers for Cuda only but not for graphics display. The default settings messes the OpenGL display drivers) and you need to do a fresh install (again there are many messy ways to escape without a fresh install but lets try to make it correct from the start anyways).
Instructions on Ubuntu 16.04/14.04 after a fresh install
