Experiments for paper on loop technique.

- ring: single MPI program where processes send right, receive left, N times.
  verify absence of potential deadlock for any N

- diffusion_simple: two programs for 1d-diffusion, one sequential, one MPI.
  verify functional equivalence.

- mean: two sequential programs for computing the mean (average) of elements 
  of array of doubles.  Verify functional equivalence.

- fib: two sequential programs for computing phi (golden ratio) using
  Fibonacci sequence to withing a given tolerance using while loop.
  Verify functional equivalence.

- matrix: a single sequential program for addings two NxN matrices.  Verify
  functional correctness for all N.

- nested: two sequential programs for computing the sum_i=1^n\sum_j=0^(i^2) ij.
  verify functional equivalence for all N

- simple: collective, a multiprocess program where each proc loops N times.
  assert i==N at end.

