Abstract: Based on the integration of the genetic algorithm (GA) and the simulated annealing
algorithm, an improved lowest horizontal line (ILHL) algorithm is presented in order to improve
utilization and stability of the rectangular packing algorithm. In this algorithm, a signed decimal
encoding is utilized to generate the gene sequence in accordance with the length-width ratio and the
area of the rectangle, which is employed to establish the initial population. The improved lowest
horizontal line algorithm adopts the best individuals from a number of random sequences with
different nesting orders and layout sizes, uses utilization rate as the fitness function and reduces the
idle area. In this paper, a contrast experiment is operated to compare ten groups of rectangular data
randomly generated by ILHL with those generated by GA proposed in the current literature. The
experiment results show that our algorithm (ILHL) can effectively improve the utilization rate and
time efficiency of the packing results.

Key words: rectangular packing, genetic algorithm, simulated annealing algorithm, improved lowest horizontal line