# Rev Language Reference

## mvCollapseExpandFossilBranch

### Usage

mvCollapseExpandFossilBranch(TimeTree tree, RealPos origin, RealPos weight, Probability tuneTarget)

### Arguments

 tree : TimeTree ( pass by reference) The tree on which this moves operates on. It should be a fossil tree! origin : RealPos (pass by reference) The variable for the origin of the process giving a maximum age for the new fossil attachement time. weight : RealPos (pass by value) The weight how often on average this move will be used per iteration. Default : 1 tuneTarget : Probability (pass by value) The acceptance probability targeted by auto-tuning. Default : 0.44