Can't set discrete graphics on for external display
The screen on this article does not match what I see anymore. Instead I get
System Version: OS X 10.11.6 (15G31)
Kernel Version: Darwin 15.6.0
By default, an external display will always engage dedicated graphics. "About this Mac" will reveal which GPU is in use. Or, you can look at an app called gfxcardstatus to show which GPU is in use, and provide some control over which is used.