BeamContact2D queries

[kamyarsa]

Hello,
I am trying to model a retaining wall using dispbeamcol and the BeamContact2D interface. Can anyone help me with its force queries?
The terms are "force", "frictionforce", "scalarforce", and "masterforce". Could anyone tell what they exactly are? wiki's explanation is not enough in my opinion.

For example how the scalar are calculated?
Or why the masteforce values are different from force values we output from the wall elements?

Thank you for your help!