Program is now running

    - Had to fix many silly mistakes. Mostly related to mixing up
      square grid indexing with compressed circular indexing. Also
      some silly mistakes with probabilities.

    - Output is not expected. It seems that the discharge pattern
      maintains a circular shape as it expands outwards. Rather than
      penalising hops back to the centre these hops seem to occur quite
      readily. Perhaps my boundary conditions are wrong. Maybe it should
      be 1.0 in the centre and 0.0 on the boundary?