anchor.diff:  !*calc_press_area:* Calculates new radii based on pressure area relnships
   
   subroutine calc_press_area(grav_type,grav_vect,KOUNT,depvar_at_node,prq_solution,&
  -    mesh_dof,ptrans,vessel_type,elasticity_parameters,pleural_density)
  +    mesh_dof,vessel_type,elasticity_parameters,mechanics_type,mechanics_parameters)
   
       use indices
       use arrays,only: dp,num_nodes,num_elems,elem_field,elem_nodes,node_xyz
       use diagnostics, only: enter_exit
       character(len=60), intent(in) :: grav_type
       character(len=60), intent(in) :: vessel_type
  +    character(len=60), intent(in) :: mechanics_type
       real(dp), intent(in) :: grav_vect(3)
       integer,intent(in) :: KOUNT,mesh_dof
       integer,intent(in) :: depvar_at_node(num_nodes,0:2,2)
       real(dp),intent(in) ::  prq_solution(mesh_dof,2)
  -    real(dp),intent(in) :: elasticity_parameters(3),ptrans,pleural_density
  +    real(dp),intent(in) :: elasticity_parameters(3),mechanics_parameters(2)
   
   !local variables
       integer :: nj,np,ne,ny,nn
  
positive.code: 
  inletbc=2266.0_dp
  outletbc=666.7_dp
  ptrans=5.33_dp
  pleural_density=0.25_dp*0.1e-5_dp !kg/mm**3
  
  !!---------DESCRIPTION OF IMPORTANT PARAMETERS-----------
  !viscosity: fluid viscosity
  
negative.code: !
  !
  !vessel_type:
    !rigid, no elasticity, no parameters required
    !elastic_g0_beta, R=R0*((Ptm/G0)+1.d0)^(1.d0/elasticity_parameters(2)),with an optional maximum pressure beyond which the vessel radius is constant three parameters, g0, elasticity_parameters(2), elasticity_parameters(3)
    !elastic alpha,  R=R0*(alpha*Ptm+1.d0), up to a limit elasticity_parameters(3) two parameters alpha, elasticity_parameters(3)
    !elastic_hooke, two parameters E and h,R=R0+3.0_dp*R0**2*Ptm/(4.0_dp*E*h*R0)
  
  !mechanics type:
    !linear two parmeters, transpulmonary pressure (average) and pleural density (gradient)
    !mechanics, two parameters, pressure and stretch fields
  
  
  !bc_type: can be pressure (at inlet and outlets) or flow (flow at inlet pressure at outlet).
  mesh_type='simple_tree'
  vessel_type='elastic_g0_beta'
  mechanics_type='linear'
  bc_type='pressure'
  grav_type='on'
  