Arguments

ierr 		 return value, operation failed when returnvalue negative

cctkGH 		 grid hierarchy pointer

stencil_size(dim) 		 array of size dim(dimension of the grid function).


To how many points from the outer boundary to apply the boundary condition. 

speed 		 wave speed used for boundary condition ($v$)

limit 		 asymptotic value of function at infinity ($f_0$)

variable_name 		 the name of the grid function  to which the boundary condition will be applied

variable_name_past 		 The name of the grid function containing the values on the past time level,


needed to calculate the boundary condition.

group_name 		 the name of the group to which the boundary condition will be applied

group_name_past 		 is the name of the group containing the grid functions on the past time level,


needed to calculate the boundary condition.

variable_index 		 the index of the grid function to which the boundary condition will be applied

variable_index_past 		 the index of the grid function containing the values on the past time level,


needed to calculate the boundary condition.

group_index 		 the index of the group to which the boundary condition will be applied

group_index_past 		 the index of the group containing the values on the past time level,


needed to calculate the boundary condition.