lock triangular form.
 
<b><u>Utilities.</u></b>
  cutsize        - Find or count edges cut by a partition.
  other          - Other side of a partition, or change representations.
  intersection   - Intersection of two sets.
  union          - Union of two sets.
  fiedler        - Fiedler vector of a graph.
  laplacian      - Laplacian matrix of a graph.
  components     - Connected components of a graph.
  contract       - Condense a graph according to a given block structure.
  distances      