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2.09 (fspring is approximately proportional to that individuals) 249.94 694.95 P0.83 (performance. As there is no constraint on an individual\325) 135.65 680.95 P0.83 (s performance in a given) 409.76 680.95 P6.32 (generation, highly \336t individuals in early generations can dominate the) 135.65 666.95 P5.59 (reproduction causing rapid conver) 135.65 652.95 P5.59 (gence to possibly sub-optimal solutions.) 316.4 652.95 P0.26 (Similarly) 135.65 638.95 P0.26 (, if there is little deviation in the population, then scaling provides only a) 179.52 638.95 P(small bias towards the most \336t individuals.) 135.65 624.95 T0.33 (Baker [14] suggests that by limiting the reproductive range, so that no individuals) 135.65 598.95 P-0.13 (generate an excessive number of of) 135.65 584.95 P-0.13 (fspring, prevents premature conver) 304.27 584.95 P-0.13 (gence. Here,) 471.52 584.95 P0.97 (individuals are assigned a \336tness according to their rank in the population rather) 135.65 570.95 P0.72 (than their raw performance. One variable,) 135.65 556.95 P0 F0.72 (MAX) 343.76 556.95 P2 F0.72 (, is used to determine the bias, or) 368.41 556.95 P0 F0.65 (selective pr) 135.65 542.95 P0.65 (essur) 190.81 542.95 P0.65 (e) 215.68 542.95 P2 F0.65 (, towards the most \336t individuals and the \336tness of the others is) 221.01 542.95 P(determined by the following rules:) 135.65 528.95 T(\245) 157.25 502.95 T0 F(MIN) 164.44 502.95 T2 F( = 2.0 -) 186.43 502.95 T0 F(MAX) 224.17 502.95 T2 F(\245) 157.25 482.95 T0 F(INC) 164.44 482.95 T2 F( = 2.0) 184.44 482.95 T4 F(\264) 215.19 482.95 T2 F( \050) 221.77 482.95 T0 F(MAX) 228.76 482.95 T2 F( -1.0\051 /) 253.41 482.95 T0 F(N) 288.72 482.95 T0 10 Q(ind) 296.72 479.95 T2 12 Q(\245) 157.25 462.95 T0 F(LOW) 164.44 462.95 T2 F( =) 189.76 462.95 T0 F(INC) 202.52 462.95 T2 F( / 2.0) 222.52 462.95 T2.81 (where) 135.65 442.95 P0 F2.81 (MIN) 170.75 442.95 P2 F2.81 ( is the lower bound,) 192.74 442.95 P0 F2.81 (INC) 304.71 442.95 P2 F2.81 ( is the dif) 324.7 442.95 P2.81 (ference between the \336tness of) 377.88 442.95 P0.97 (adjacent individuals and) 135.65 428.95 P0 F0.97 (LOW) 258.13 428.95 P2 F0.97 ( is the expected number of trials \050number of times) 283.45 428.95 P1.2 (selected\051 of the least \336t individual.) 135.65 414.95 P0 F1.2 (MAX) 311.73 414.95 P2 F1.2 ( is typically chosen in the interval [1.1,) 336.38 414.95 P0.66 (2.0]. Hence, for a population size of) 135.65 400.95 P0 F0.66 (N) 316.12 400.95 P0 10 Q0.55 (ind) 324.11 397.95 P2 12 Q0.66 ( = 40 and) 336.89 400.95 P0 F0.66 (MAX) 387.59 400.95 P2 F0.66 ( = 1.1, we obtain) 412.24 400.95 P0 F0.66 (MIN) 499.24 400.95 P2 F0.66 ( =) 521.23 400.95 P-0.18 (0.9,) 135.65 386.95 P0 F-0.18 (INC) 156.46 386.95 P2 F-0.18 ( = 0.05 and) 176.45 386.95 P0 F-0.18 (LOW) 232.81 386.95 P2 F-0.18 ( = 0.025. The \336tness of individuals in the population may) 258.13 386.95 P(also be calculated directly as,) 135.65 372.95 T(,) 439.73 335.53 T(where) 135.65 299.28 T0 F(x) 167.95 299.28 T0 10 Q(i) 173.27 296.28 T2 12 Q( is the position in the ordered population of individual) 176.05 299.28 T0 F(i) 437.9 299.28 T2 F(.) 441.24 299.28 T-0.04 (Objective functions must be created by the user) 135.65 273.28 P-0.04 (, although a number of example m-) 363.03 273.28 P0.7 (\336les are supplied with the T) 135.65 259.28 P0.7 (oolbox that implement common test functions. These) 271.91 259.28 P0.98 (objective functions all have the \336lename pre\336x) 135.65 245.28 P3 F2.36 (obj) 370.71 245.28 P2 F0.98 (. The T) 392.3 245.28 P0.98 (oolbox supports both) 428.4 245.28 P1.65 (linear and non-linear ranking methods,) 135.65 231.28 P3 F3.97 (ranking) 333.11 231.28 P2 F1.65 (, and includes a simple linear) 383.48 231.28 P1.26 (scaling function,) 135.65 217.28 P3 F3.02 (scaling) 221.11 217.28 P2 F1.26 (, for completeness. It should be noted that the linear) 271.49 217.28 P-0.14 (scaling function is not suitable for use with objective functions that return negative) 135.65 203.28 P(\336tness values.) 135.65 189.28 T1 16 Q(Selection) 135.65 160.61 T2 12 Q0.46 (Selection is the process of determining the number of times, or) 135.65 133.28 P0 F0.46 (trials) 445.13 133.28 P2 F0.46 (, a particular) 470.46 133.28 P1.43 (individual is chosen for reproduction and, thus, the number of of) 135.65 119.28 P1.43 (fspring that an) 459.51 119.28 P224.57 321.28 439.73 354.95 C0 12 Q0 X0 K(F) 225.57 335.53 T(x) 240.7 335.53 T0 9 Q(i) 246.49 331.75 T4 12 Q(\050) 235.6 335.53 T(\051) 249.59 335.53 T2 F(2) 274.17 335.53 T0 F(M) 292.75 335.53 T(A) 303.45 335.53 T(X) 311.48 335.53 T4 F(-) 283.17 335.53 T2 F(2) 331.39 335.53 T0 F(M) 345.2 335.53 T(A) 355.89 335.53 T(X) 363.93 335.53 T2 F(1) 383.84 335.53 T4 F(-) 374.26 335.53 T(\050) 340.1 335.53 T(\051) 390.45 335.53 T0 F(x) 404.51 345.75 T0 9 Q(i) 410.29 341.97 T2 12 Q(1) 425.37 345.75 T4 F(-) 415.79 345.75 T0 F(N) 398.14 327.91 T0 9 Q(i) 406.61 324.13 T(n) 409.63 324.13 T(d) 414.66 324.13 T2 12 Q(1) 431.73 327.91 T4 F(-) 422.15 327.91 T(+) 321.81 335.53 T(=) 261.59 335.53 T398.14 338.12 437.48 338.12 2 L0.33 H0 ZN-8.35 24.95 603.65 816.95 CFMENDPAGE%%EndPage: "9" 10%%Page: "10" 10595.3 841.9 0 FMBEGINPAGE0 10 Q0 X0 K(Genetic Algorithm Toolbox User\325s Guide) 63.65 61.61 T(1-10) 513.33 61.29 T2 12 Q-0.28 (individual will produce. The selection of individuals can be viewed as two separate) 135.65 736.95 P(processes:) 135.65 722.95 T(1\051) 135.65 696.95 T0.93 (determination of the number of trials an individual can expect to receive,) 171.65 696.95 P(and) 171.65 682.95 T(2\051) 135.65 662.95 T2.6 (conversion of the expected number of trials into a discrete number of) 171.65 662.95 P(of) 171.65 648.95 T(fspring.) 181.42 648.95 T-0.07 (The \336rst part is concerned with the transformation of raw \336tness values into a real-) 135.65 628.95 P0.47 (valued expectation of an individual\325) 135.65 614.95 P0.47 (s probability to reproduce and is dealt with in) 310.06 614.95 P0.51 (the previous subsection as \336tness assignment. The second part is the probabilistic) 135.65 600.95 P-0.19 (selection of individuals for reproduction based on the \336tness of individuals relative) 135.65 586.95 P3.05 (to one another and is sometimes known as) 135.65 572.95 P0 F3.05 (sampling) 365.89 572.95 P2 F3.05 (. The remainder of this) 409.87 572.95 P2.11 (subsection will review some of the more popular selection methods in current) 135.65 558.95 P(usage.) 135.65 544.95 T-0.17 (Baker [15] presented three measures of performance for selection algorithms,) 135.65 518.95 P0 F-0.17 (bias) 508.66 518.95 P2 F-0.17 (,) 528.65 518.95 P0 F3.37 (spr) 135.65 504.95 P3.37 (ead) 150.53 504.95 P2 F3.37 ( and) 167.85 504.95 P0 F3.37 (ef\336ciency) 197.9 504.95 P2 F3.37 (. Bias is de\336ned as the absolute dif) 242.41 504.95 P3.37 (ference between an) 432.34 504.95 P4.34 (individual\325) 135.65 490.95 P4.34 (s actual and expected selection probability) 187.63 490.95 P4.34 (. Optimal zero bias is) 412.04 490.95 P1.03 (therefore achieved when an individual\325) 135.65 476.95 P1.03 (s selection probability equals its expected) 326.95 476.95 P(number of trials.) 135.65 462.95 T-0.05 (Spread is the range in the possible number of trials that an individual may achieve.) 135.65 436.95 P0.71 (If) 135.65 422.95 P0 F0.71 (f\050i\051) 147.34 422.95 P2 F0.71 ( is the actual number of trials that individual) 162 422.95 P0 F0.71 (i) 383.91 422.95 P2 F0.71 ( receives, then the \322minimum) 387.24 422.95 P(spread\323 is the smallest spread that theoretically permits zero bias, i.e.) 135.65 408.95 T0.3 (where) 135.65 321.65 P0 F0.3 (et\050i\051) 168.24 321.65 P2 F0.3 ( is the expected number of trials of individual) 188.23 321.65 P0 F0.3 (i) 412.42 321.65 P2 F0.3 (,) 415.76 321.65 P0.3 ( is the \337oor of) 463.16 321.65 P1.64 (et\050i\051 and) 135.65 307.65 P1.64 ( is the ceil. Thus, while bias is an indication of accuracy) 223.32 307.65 P1.64 (, the) 509.36 307.65 P(spread of a selection method measures its consistency) 135.65 293.65 T(.) 393.02 293.65 T0.88 (The desire for ef) 135.65 267.65 P0.88 (\336cient selection methods is motivated by the need to maintain a) 217.67 267.65 P1.72 (GAs overall time complexity) 135.65 253.65 P1.72 (. It has been shown in the literature that the other) 279.61 253.65 P4.96 (phases of a GA \050excluding the actual objective function evaluations\051 are) 135.65 239.65 P1 (O\050L) 135.65 225.65 P2 10 Q0.83 (ind) 155.63 222.65 P2 12 Q1 (.N) 168.4 225.65 P2 10 Q0.83 (ind) 180.06 222.65 P2 12 Q1 (\051 or better time complexity) 192.83 225.65 P1 (, where L) 324.64 225.65 P2 10 Q0.83 (ind) 372.27 222.65 P2 12 Q1 ( is the length of an individual) 385.05 225.65 P0.71 (and N) 135.65 211.65 P2 10 Q0.59 (ind) 165.33 208.65 P2 12 Q0.71 ( is the population size. The selection algorithm should thus achieve zero) 178.1 211.65 P1.51 (bias whilst maintaining a minimum spread and not contributing to an increased) 135.65 197.65 P(time complexity of the GA.) 135.65 183.65 T1 14 Q(Roulette Wheel Selection Methods) 135.65 156.31 T2 12 Q8.61 (Many selection techniques employ a \322roulette wheel\323 mechanism to) 135.65 129.65 P-0.14 (probabilistically select individuals based on some measure of their performance. A) 135.65 115.65 P2.72 (real-valued interval,) 135.65 101.65 P0 F2.72 (Sum) 240.67 101.65 P2 F2.72 (, is determined as either the sum of the individuals\325) 261.32 101.65 P261.26 343.65 406.04 390.95 C0 12 Q0 X0 K(f) 262.26 364.71 T(i) 273.4 364.71 T4 F(\050) 268.3 364.71 T(\051) 277.34 364.71 T0 F(e) 312.75 365.19 T(t) 318.78 365.19 T(i) 329.92 365.19 T4 F(\050) 324.82 365.19 T(\051) 333.86 365.19 T0 F(e) 357.85 365.19 T(t) 363.89 365.19 T(i) 375.03 365.19 T4 F(\050) 369.92 365.19 T(\051) 378.97 365.19 T(,) 345.86 365.19 T(\376) 394.67 350.05 T(\375) 394.67 362.17 T(\374) 394.67 374.29 T(\356) 299.88 350.05 T(\355) 299.88 362.17 T(\354) 299.88 374.29 T(\316) 286.33 364.71 T307.75 362.2 307.75 373.4 2 L0.33 H0 ZN307.75 362.2 310.75 362.2 2 LN343.86 362.2 343.86 373.4 2 LN343.86 362.2 340.86 362.2 2 LN352.85 362.2 352.85 373.4 2 LN352.85 373.4 355.85 373.4 2 LN388.96 362.2 388.96 373.4 2 LN388.96 373.4 385.96 373.4 2 LN-8.35 24.95 603.65 816.95 C422.05 316.65 463.16 330.85 C0 12 Q0 X0 K(e) 429.05 321.65 T(t) 435.08 321.65 T(i) 446.23 321.65 T4 F(\050) 441.12 321.65 T(\051) 450.17 321.65 T424.05 318.65 424.05 329.85 2 L0.33 H0 ZN424.05 318.65 427.05 318.65 2 LN460.16 318.65 460.16 329.85 2 LN460.16 318.65 457.16 318.65 2 LN-8.35 24.95 603.65 816.95 C182.22 302.65 223.32 316.85 C0 12 Q0 X0 K(e) 189.22 307.65 T(t) 195.25 307.65 T(i) 206.39 307.65 T4 F(\050) 201.29 307.65 T(\051) 210.33 307.65 T184.22 304.65 184.22 315.85 2 L0.33 H0 ZN184.22 315.85 187.22 315.85 2 LN220.32 304.65 220.32 315.85 2 LN220.32 315.85 217.32 315.85 2 LN-8.35 24.95 603.65 816.95 CFMENDPAGE%%EndPage: "10" 11%%Page: "11" 11595.3 841.9 0 FMBEGINPAGE0 10 Q0 X0 K(Genetic Algorithm Toolbox User\325s Guide) 63.65 61.61 T(1-11) 513.33 61.29 T2 12 Q1.17 (expected selection probabilities or the sum of the raw \336tness values over all the) 135.65 736.95 P0.26 (individuals in the current population. Individuals are then mapped one-to-one into) 135.65 722.95 P1.69 (contiguous intervals in the range [0,) 135.65 708.95 P0 F1.69 (Sum) 321.33 708.95 P2 F1.69 (]. The size of each individual interval) 341.98 708.95 P-0.14 (corresponds to the \336tness value of the associated individual. For example, in Fig. 2) 135.65 694.95 P1.38 (the circumference of the roulette wheel is the sum of all six individual\325) 135.65 680.95 P1.38 (s \336tness) 491.95 680.95 P1.76 (values. Individual 5 is the most \336t individual and occupies the lar) 135.65 666.95 P1.76 (gest interval,) 467.93 666.95 P1.97 (whereas individuals 6 and 4 are the least \336t and have correspondingly smaller) 135.65 652.95 P1.31 (intervals within the roulette wheel. T) 135.65 638.95 P1.31 (o select an individual, a random number is) 318.59 638.95 P1.88 (generated in the interval [0,) 135.65 624.95 P0 F1.88 (Sum) 280.29 624.95 P2 F1.88 (] and the individual whose segment spans the) 300.94 624.95 P1.11 (random number is selected. This process is repeated until the desired number of) 135.65 610.95 P(individuals have been selected.) 135.65 596.95 T-0.04 (The basic roulette wheel selection method is stochastic sampling with replacement) 135.65 570.95 P4.89 (\050SSR\051. Here, the segment size and selection probability remain the same) 135.65 556.95 P3.36 (throughout the selection phase and individuals are selected according to the) 135.65 542.95 P0.48 (procedure outlined above. SSR gives zero bias but a potentially unlimited spread.) 135.65 528.95 P(Any individual with a segment size > 0 could entirely \336ll the next population.) 135.65 514.95 T3.91 (Stochastic sampling with partial replacement \050SSPR\051 extends upon SSR by) 135.65 271.94 P3.1 (resizing an individual\325) 135.65 257.94 P3.1 (s segment if it is selected. Each time an individual is) 249.12 257.94 P1.33 (selected, the size of its segment is reduced by 1.0. If the segment size becomes) 135.65 243.94 P2.15 (negative, then it is set to 0.0. This provides an upper bound on the sprea
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