output of `xrandr -q` with displayport plugged in, but not active.
==================================================================

Screen 0: minimum 320 x 200, current 1680 x 1050, maximum 8192 x 8192
DVI-0 unknown connection (normal left inverted right x axis y axis)
   1024x768       60.0
   800x600        60.3
   640x480        59.9
   512x384       120.0
   400x300       120.6
   320x240       120.1
LVDS connected 1680x1050+0+0 (normal left inverted right x axis y axis) 331mm x 207mm
   1680x1050      60.1*+   50.1
   1400x1050      60.0
   1280x1024      59.9
   1440x900       59.9
   1280x960       59.9
   1280x854       59.9
   1280x800       59.8
   1280x720       59.9
   1152x768       59.8
   1024x768       59.9
   800x600        59.9
   848x480        59.7
   720x480        59.7
   640x480        59.4
DisplayPort-0 connected (normal left inverted right x axis y axis)
   1680x1050      59.9 +
   1280x1024      75.0     60.0
   1152x864       75.0
   1024x768       75.1     60.0
   800x600        75.0     60.3
   640x480        75.0     60.0
   720x400        70.1
VGA-0 disconnected (normal left inverted right x axis y axis)

===========================
the xrandr command executed by my "setup screen" script, and the `xrandr -q` output
===========================

xrandr --output LVDS --primary --output LVDS --mode 1680x1050 --output DisplayPort-0 --mode 1680x1050 --right-of LVDS --output VGA-0 --off
Screen 0: minimum 320 x 200, current 3360 x 1050, maximum 8192 x 8192
DVI-0 unknown connection (normal left inverted right x axis y axis)
   1024x768       60.0
   800x600        60.3
   640x480        59.9
   512x384       120.0
   400x300       120.6
   320x240       120.1
LVDS connected 1680x1050+0+0 (normal left inverted right x axis y axis) 331mm x 207mm
   1680x1050      60.1*+   50.1
   1400x1050      60.0
   1280x1024      59.9
   1440x900       59.9
   1280x960       59.9
   1280x854       59.9
   1280x800       59.8
   1280x720       59.9
   1152x768       59.8
   1024x768       59.9
   800x600        59.9
   848x480        59.7
   720x480        59.7
   640x480        59.4
DisplayPort-0 connected 1680x1050+1680+0 (normal left inverted right x axis y axis) 474mm x 296mm
   1680x1050      59.9*+
   1280x1024      75.0     60.0
   1152x864       75.0
   1024x768       75.1     60.0
   800x600        75.0     60.3
   640x480        75.0     60.0
   720x400        70.1
VGA-0 disconnected (normal left inverted right x axis y axis)