Convergence of the gradient algorithm for linear regression models in the continuous and discrete time cases

We establish convergence to zero of the solutions of \dot \tilde θ(t) = −φ(t)φ(t) \tilde θ(t) or \tilde θ(t) = \tilde θ(t − 1) − φ(t)φ(t) \tilde θ(t − 1) under a possibly " vanishing persistent " excitation condition.