$useDDCCPBC

$useDDCCPBC is the command to setup periodic boundary condition.
Format:

$useDDCCPBC
1 xleft  xrigth yleft  yrigth
txtfilename

Example:

$useDDCCPBC 
1 0 30e-07 0 30e-07 
LED_PBC.txt

xleft is the left x point for periodic boundary condition. xright is the right x point. xleft and xright usually correspond to the mesh boundary.
yleft is the left y point for periodic boundary condition. yright is the right y point. yleft and xright usually correspond to the mesh boundary.
txtfilename will be automatically generated every time.