使用Matlab实现一个GA算法求解极值的函数:f = -200*exp(-0.05*x)*sin(x);求解区间[-2, 2]
时间: 2024-03-15 20:45:54 浏览: 15
好的,我会尽力回答您的问题。首先,您需要定义适应度函数,即目标函数 $f(x)$ 在给定区间 $[-2, 2]$ 上的极值问题。根据您提供的函数,适应度函数可以写成如下形式:
```matlab
function y = fitness(x)
y = -200 * exp(-0.05*x) * sin(x);
end
```
接下来,您需要定义 GA 算法的参数,如种群大小、交叉率、变异率等。这里我们将种群大小设置为 50,交叉率为 0.8,变异率为 0.01,最大迭代次数为 100。
```matlab
popSize = 50;
crossoverRate = 0.8;
mutationRate = 0.01;
maxIterations = 100;
```
然后,您需要定义 GA 算法的主体框架,包括初始化种群、计算适应度、选择、交叉和变异等步骤。这里我们采用基本的遗传算法(GA)实现,具体代码如下:
```matlab
% 初始化种群
pop = rand(popSize, 1) * 4 - 2; % 随机生成种群,范围为 [-2, 2]
bestFitness = Inf;
bestIndividual = [];
for i = 1:maxIterations
% 计算适应度
fitnessValues = fitness(pop);
[minFitness, minIndex] = min(fitnessValues);
% 保存最优个体
if minFitness < bestFitness
bestFitness = minFitness;
bestIndividual = pop(minIndex);
end
% 选择
selected = selection(pop, fitnessValues);
% 交叉
offspring = crossover(selected, crossoverRate);
% 变异
offspring = mutation(offspring, mutationRate);
% 更新种群
pop = [pop; offspring];
fitnessValues = [fitnessValues; fitness(offspring)];
[~, rank] = sort(fitnessValues, 'descend');
pop = pop(rank(1:popSize));
end
fprintf('最优解为 x = %f, f(x) = %f\n', bestIndividual, bestFitness);
```
最后,您需要定义选择、交叉和变异等具体函数。这里我们采用轮盘赌选择、单点交叉和随机变异。具体代码如下:
```matlab
% 轮盘赌选择
function selected = selection(pop, fitnessValues)
fitnessValues = fitnessValues - min(fitnessValues) + eps;
fitnessSum = sum(fitnessValues);
fitnessProb = fitnessValues / fitnessSum;
probSum = cumsum(fitnessProb);
selected = zeros(size(pop));
for i = 1:length(pop)
r = rand();
for j = 1:length(pop)
if r <= probSum(j)
selected(i) = pop(j);
break;
end
end
end
end
% 单点交叉
function offspring = crossover(selected, crossoverRate)
offspring = zeros(size(selected));
for i = 1:2:length(selected)
if rand() < crossoverRate
pos = randi([1, length(selected)-1]);
offspring(i) = [selected(i, 1:pos), selected(i+1, pos+1:end)];
offspring(i+1) = [selected(i+1, 1:pos), selected(i, pos+1:end)];
else
offspring(i) = selected(i);
offspring(i+1) = selected(i+1);
end
end
end
% 随机变异
function offspring = mutation(selected, mutationRate)
offspring = selected;
for i = 1:length(selected)
if rand() < mutationRate
offspring(i) = offspring(i) + randn() * 0.1;
if offspring(i) < -2
offspring(i) = -2;
elseif offspring(i) > 2
offspring(i) = 2;
end
end
end
end
```
以上就是使用 Matlab 实现 GA 算法求解极值的函数的完整代码。希望能对您有所帮助!