TUBEPLOT  TUBEPLOT Creates a Tubeplot


Usage
 
 This tubeplot function is from the tubeplot package
 written by Anders Sandberg. The simplest syntax for the
 tubeplot routine is
 
     tubeplot(x,y,z)
 
 plots the basic tube with radius 1, where x,y,z are
 vectors that describe the tube.  If the radius of the
 tube is to be varied, use the second form
 
     tubeplot(x,y,z,r) 
 
 which plots the basic tube with variable radius r (either 
 a vector or a scalar value).  The third form allows you
 to specify the coloring using a vector of values:
 
     tubeplot(x,y,z,r,v)
 
 where the coloring is now dependent on the values in the 
 vector v.  If you want to create a tube plot with 
 a greater degree of tangential subdivisions (i.e.,
 the tube is more circular, use the form
 
     tubeplot(x,y,z,r,v,s)
 
 where s is the number of tangential subdivisions (default is 6)
 You can also use tubeplot to calculate matrices to feed to mesh
 and surf.
 
     [X,Y,Z]=tubeplot(x,y,z)
 
 returns N x 3 matrices suitable for mesh or surf.
 
 Note that the tube may pinch at points where the normal and binormal 
 misbehaves. It is suitable for general space curves, not ones that 
 contain straight sections. Normally the tube is calculated using the
 Frenet frame, making the tube minimally twisted except at inflexion points.
 
 To deal with this problem there is an alternative frame:
 
     tubeplot(x,y,z,r,v,s,vec)
 
 calculates the tube by setting the normal to
 the cross product of the tangent and the vector vec. If it is chosen so 
 that it is always far from the tangent vector the frame will not twist unduly.
 