tters.<p>

The user must supply a file containing the co-ordinates for the ion channel
structure to be analyzed - in pdb format.  Atom records are read and the van der
Waals radius of each atom is set up. In the original version
the user had to supply an
initial point in the channel cavity and a vector in the rough direction of the
channel, now HOLE has the facility to make guesses for these.  
HOLE then proceeds to move the point on the plane normal to the
channel vector so as to find the largest sphere wh