【生成式模型入门】（四）：Flow Matching——从速度场学习到生成路径x t − 1 = 1 α t ( x t − 1 − α t 1 − α ˉ t ε θ ( x t , t , c ) ) + σ t z x_{t-1} = \frac{1}{\sqrt{\alpha_t}}\left( x_t - \frac{1 - \alpha_t}{\sqrt{1 - \bar\alpha_t}}\, \varepsilon_\theta(x_t, t, c) \right) + \sigma_t z xt−1=αt 1(xt−1−αˉt 1−αtεθ(xt,t,c))+