Another 15 years have gone by since the second edition of this text appeared.During this period,the rate of development in algorithms has slowed compared to any earlier period,but the increase in computational power has been astounding and shows no sign of slowing.Desktop computers can outperform the supercomputers of the early 1990s.The rate ofimprovement of computing power is such that a problem that required a year of computing time to solve 10 years ago can now be solved overnight.