code: def velvet(readsize, genomesize, numreads, K):
      
      ram = -109635 + 18977 * readsize + 86326 * genomesize + \
              233353 * numreads - 51092 * K
      print("ReadSize: {0}".format(readsize), file=sys.stderr)
      print("GenomeSize: {0}Mb".format(genomesize), file=sys.stderr)
      print("NumReads: {0}M".format(numreads), file=sys.stderr)
      print("K: {0}".format(K), file=sys.stderr)
  
      ram = human_size(ram * 1000, a_kilobyte_is_1024_bytes=True)
      print("RAM usage: {0} (MAXKMERLENGTH=31)".format(ram), file=sys.stderr)
docs: Calculate velvet memory requirement.
      <http://seqanswers.com/forums/showthread.php?t=2101>
  
      Ram required for velvetg = -109635 + 18977*ReadSize + 86326*GenomeSize +
      233353*NumReads - 51092*K
  
      Read size is in bases.
      Genome size is in millions of bases (Mb)
      Number of reads is in millions
      K is the kmer hash value used in velveth