APG算法matlab代码
时间: 2023-08-01 09:06:37 浏览: 138
APG(Accelerated Proximal Gradient)算法是一种用于优化问题的迭代算法。以下是一个简单的 MATLAB 代码实现:
假设我们要求解以下的优化问题:
```
minimize f(x)
subject to g(x) <= 0
```
其中, `f(x)` 和 `g(x)` 是可微分的凸函数。以下是 MATLAB 代码:
```matlab
function [x, obj] = apg(f, g, x0, lambda, max_iter, tol)
% f: objective function
% g: inequality constraint function
% x0: initial point
% lambda: step size
% max_iter: maximum number of iterations
% tol: tolerance
% initialization
x_prev = x0;
y_prev = x0;
t_prev = 1;
for i=1:max_iter
% gradient step
grad_f = grad(f, y_prev);
x = prox(y_prev - lambda * grad_f, lambda);
% projection step
x = proj(x, g);
% acceleration
t = (1 + sqrt(1 + 4 * t_prev^2)) / 2;
y = x + (t_prev - 1) / t * (x - x_prev);
% convergence check
if norm(y - y_prev) < tol
break;
end
% update
x_prev = x;
y_prev = y;
t_prev = t;
end
% return solution and objective value
x = y;
obj = f(x);
end
function [x] = prox(x, lambda)
% proximal operator for L1 norm
x = sign(x) .* max(abs(x) - lambda, 0);
end
function [x] = proj(x, g)
% projection operator for inequality constraint
if g(x) <= 0
% x satisfies the constraint, no need to project
return;
else
% find the projection of x onto the feasible set
f = @(t) norm(x - t*g(x))^2;
options = optimoptions('fmincon', 'Display', 'off');
x = fmincon(f, x, [], [], [], [], [], [], @(x) g(x), options);
end
end
```
在代码中,`grad` 函数计算函数 `f` 的梯度,`prox` 函数是 L1 范数的 proximal 运算符,`proj` 函数是约束条件的投影运算符。在主函数 `apg` 中,我们按照 APG 算法的步骤进行迭代,直到满足收敛条件为止。
需要注意的是,这只是一个简单的实现,可能需要根据实际问题进行修改。