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Are you sure you're not getting GAs mixed up with gradient descent? The whole point of a GA is that they're a global search. Mutation and crossover (with certai
by sadiq 19y ago
Are you sure you're not getting GAs mixed up with gradient descent? The whole point of a GA is that they're a global search. Mutation and crossover (with certain conditions) generally mean you don't get stuck in local maxima.
Of course, there are conditions on that. The quality of your RNG, the probabilities of mutation/crossover, etc..
- pixcavator 19y agoMarcus replied to that http://news.ycombinator.com/item?id=90115 http://news.ycombinator.com/item?id=90115.
- sadiq 19y agoExactly. He's describing gradient descent (and possibly simulated annealing), not a genetic algorithm. Mutation, especially burst mutation with population stagnation, is what stops you getting stuck in local maxima.
- pixcavator 19y agoIt does not matter _how_ it is done, it is still an iteration. You may have several iterations going on but at best you can expect to find several local maxima - at any given time. Further, if there is no "stagnation", how do you know that you've found a solution?
- sadiq 19y agoStagnation is the case where the best individuals in the populations fitness hasn't increased by some value for a certain period of time. I'm not sure I understand what you mean by 'a solution'? You know you've not arrived at an acceptable solution when your fitness is below your required level. Granted, you never know there is a configuration with a fitness greater than your required fitness but this is generally considered when constructing the fitness function.
- pixcavator 19y agoI understand that when a certain level of fitness is reached the procedure stops. But, it may stop too early - missing the global max. And second, it may never stop!
- sadiq 19y agoTrue. I've seen some interesting work on the latter case that produces upper and lower bounds for time to an acceptable solution but so far it seems to be limited in it's application to real world tasks. Missing the global max less of an issue, an acceptable level of fitness is generally all that's required for most applications. Though I guess there are several tasks for which a global max would be useful.