* Exercise : "Distributed matrix initialization"
  - Broadcast only

  - read matrix size n from command line
  - only processor 0 can access argc and argv
  - if argc < 2: ask for argument + everybody returns graciously
  - if n > nProcs: complain + everybody returns graciously 
  - else:     // more processes than columns
    everybody allocates M, a matrix of size 2*n x n, storage by columns
  - 0 <= i < n: 
    process_i initializes randomly the i-th column of M
  - every process prints out M  
  - process_i sends the i_th column to everyone else 
  - every process prints out M