Rest Length in Kangaroo 2

Hey!

I am trying to do different simulations for a Gridshell with the new kangaroo. I wanted to know how I can input the Rest Length so that the total lath length would remain the same even after the simulation. Also the mesh always takes the shape of a Catenary when the edge points are not anchored, do I need to change some settings for the same?

Would be great if someone could help!. 

Attaching a trial file!

Thanks!

Seeja