What is a .GCH file?

In the picture below from your blog I see a .GCH file. What is that?

That is a file with instructions for the graphics module in the GAMS IDE. It is a text file so you can look at it. The IDE can view it as text or show the results. For more information have a look at the help in IDE: HelpGAMSIDE Help TopicsGuided TourCreating Charts.