Get screen size (dynamic)

Same as get( 0, 'ScreenSize' ), but dynamic

GETSCREENSIZE Same as get( 0, 'ScreenSize' ), but dynamic

SZ = GETSCREENSIZE returns a 1x4 vector of doubles giving the size of the display in pixels, in the same way as get( 0, 'ScreenSize' ), except it reads the current settings rather than reading a static copy made at MATLAB® startup time.
From "doc rootobject_props":

"Note that the ScreenSize property is static. Its values are read only at MATLAB startup and not updated if system display settings change."

Some applications place windows based on on the display resolution, and the resolution can change - mine does when I disconnect my laptop from my external monitor.