Matlab2017b does not recognize functions in program folder

I am reworking an old program, and put the old functions in a subdir inside the main program dir. While editing, I double-click on the desired functions to open them in the editor as I need them. I rename them and save them in the main program dir. When I run the program (F5), intermittently the program crashes as Matlab (Windows 10) claims to have encountered an "Undefined function or variable". The "missing" edited functions are absolutely there. Only way to remedy this, is to restart Matlab. Any thoughts?

Answer 1

[Image Analyst]

Click on the Set path button on the Home tool ribbon tab. Then add the main folder with sub folders. Click Save and Close to add those to the permanent path.