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Answers for “为什么视频说种群规模为 50 时得不到好的解?”

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Understand why

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The video demonstrates that a smaller population size (e.g., 50) leads to worse solutions compared to a larger population (e.g., 100). Specifically, the run with population size 50 produced routes with self-crossings and a longer final path length (4823) than the previous run with population size 100(4296)100 (4296).

Conditions: Observed with fixed iterations = 100 and the same displayed interface settings.; The conclusion is based on the shown runs rather than a formal proof.; Comparison is made against the previously shown larger-population run.

Find a method

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The video recommends using a large population size to initialize with a rich set of solutions. It cites a common guideline of setting the population size to 30 to 60 times the number of cities (nn).

Conditions: nn is the number of cities.; This is a heuristic guideline mentioned in the video, not a theorem proved here.; The context is the genetic-algorithm TSP implementation.

Meet the concept

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The video points out that routes crossing over themselves (self-intersections) are a sign of a worse solution. This visual cue is paired with a longer final path length in the status bar.

Conditions: Applies to the interactive TSP visualization shown in the clip.; The context is comparing different algorithm runs or parameters.

Find a method

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The video claims that, in this playground, the genetic algorithm can efficiently solve the Traveling Salesman Problem using the default parameters. The demo shows the route improving and the path length decreasing over iterations.

Conditions: The genetic-algorithm implementation is run with the displayed default parameters.; The problem instance is the one shown in the visualization.; The word "efficiently" is qualitative here; no formal efficiency metric or runtime bound is provided.

Meet the concept

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The Machine Learning Playground implements two approaches for TSP: a genetic algorithm and a method based on an elastic neural network together with a self-organization map. The video primarily demonstrates the genetic-algorithm page in detail.

Conditions: The context is the Machine Learning Playground TSP demo.; The approaches are implemented as interactive web pages.

Meet the concept

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In the genetic-algorithm TSP demo, greedy crossover uses a heuristic rule that tries to choose the nearest unvisited city as the next move. This approach is presented as a way to quickly obtain an effectively short route.

Conditions: Used inside the genetic-algorithm TSP implementation.; The crossover option is enabled (greedy crossover: true).; At each step, the next city is chosen by nearest-unvisited-city preference.