Fig. 7. Setup and results of three truss optimization problems with different numbers of bars (equal to the numbers of design variables).

a Illustration of an antenna tower, an exemplary application of truss structures. b Illustration of the problem setup: minimizing total weight through changing the size of each bar, subject to stress and displacement constraints. The block is repeated until the given number of bars is reached. c–e Dimensionless weight $\tilde{W}$ versus the number of accumulated training samples n_train. SOLO denotes our proposed method. BA denotes Bat Algorithm. The numbers of bars for these three sub-figures are 72, 432, and 1008, respectively. Each experiment is repeated five times; the curves denote the mean and the shadows denote the standard deviation.