Starting population

The selection of strings for the tournament is random, thus the results may vary each time the process is performed on a given starting population. This unpredictable selection of strings is the second time that random numbers have been used in the algorithm (the first was in the construction of the strings in the initial population) and random numbers will return shortly. It may seem surprising that random numbers are needed when the problem to be solved has a definite (albeit, still unknown) solution, but their use is a common feature in AI methods and, in fact, is fundamental to the operation of several of them. 

At the heart of the GA are evolutionary operators These are a survival of the fittest operator, and a pair of modification operators whose role is to create new strings. To apply the first of these operators, the fitter members of the starting population are selected preferentially as parents for the next generation. This, of course, requires that we know what is meant by, and can calculate, the fitness of each string. 

Selection has improved the average string fitness, but all strings are just copies of members of the starting population—no new solutions have yet been created. To fashion new, and potentially better, solutions,... 

A chemical subject to cometabolism. .. is transformed slowly, and the rate of conversion does not increase with time [low starting population in soils and water and no growth]. 

Scientists frequently express Equation 3-4 in terms of half-life ( 1/2), which is the time required for one half of the population of unstable atoms to decay. In other words, after one half-life, the rate of particles emitted has decreased to one half the rate of the starting population of unstable atoms. Substitution in Equation 3-4 yields Equation 3-5 ... 

A population of individuals is required for the EA to work on, so let us begin by making that. A portion of our random starting population of lighthouses is shown in Fig. 4, in which light-emitting blocks are shown cross-hatched and structural building blocks are shaded. 

On the roulette wheel, each string is allocated a segment whose size is proportional to the string s fitness (Fig. 10). The wheel is spun, and the string into whose slot the imaginary roulette ball falls is selected to be copied once into the new population. The process is repeated until the new population is equal in size to the starting population. 

In helium droplets, spectroscopy is usually performed in the infrared [22-25]. Resonant absorption by specific vibrational modes implies heating, resulting in helium atoms boiling off the droplets, recorded in a mass spectrometer or with a bolometer. The temperature in helium droplets is lower than in supersonic expansions and the cooling is so fast as essentially to freeze the starting population distribution. The starting temperatures need not be elevated much above room temperature because pick-up sources do not require very high gas densities. 

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