Plot a "graph theoretic" graph.

  GPLOT(A,xy) plots the graph specified by A and xy.

  A graph, G, is a set of nodes numbered from 1 to n,

  and a set of connections, or edges, between them.

  In order to plot G, two matrices are needed.

  The adjacency matrix, A, has a(i,j) nonzero if and

  only if node i is connected to node j.  The coordinates

  array, xy, is an n-by-2 matrix with the position for

  node i in the i-th row, xy(i,:) = [x(i) y(i)].



  GPLOT(A,xy,lc) uses line type and color instead of the 

  default, 'r-'.   For example, lc = 'g:'.  See PLOT3DFTRE7.



  [X,Y] = GPLOT(A,xy) returns the NaN-punctuated vectors

  X and Y without actually generating a plot. These vectors

  can be used to generate the plot at a later   time if desired.