For internal use only – not to be called by 'mrds' or 'Distance' users
directly.
     
    
    Usage
    adj.cos(distance, scaling, adj.order)
 
    
    Arguments
- distance
- perpendicular distance vector/scalar 
- scaling
- scale parameter 
- adj.order
- the adjustment order 
 
    
    Value
    scalar or vector containing the cosine adjustment term for every
value in distance argument