CRACKPATTERN Create a (bounded) crack pattern tessellation.

   E = crackPattern(BOX, POINTS, ALPHA)
   create a crack propagation pattern wit following parameters :
   - pattern is bounded by area BOX given by [xmin xmax ymin ymax].
   - each crack originates from points given in POINTS
   - direction of each crack is given by array ALPHA
   - a crack stop when it reaches another already created crack. 
   - all cracks stop when they reach the border of the frame, given by box
   (a serie of 4 points).
   The result is a collection of edges, in the form [x1 y1 x2 y2].

   E = crackPattern(BOX, POINTS, ALPHA, SPEED)
   Also specify speed of propagation of each crack.


   See the result with :
     figure;
     drawEdge(E);

   See also 
     drawEdge

Package: matgeom