A new method for solving numerically backward parabolic problems is proposed. As usual for this kind of ill posed problems, it is assumed that an a priori bound for the solution is available. The algorithm consists of two basic steps. First, a standard forward integration is performed, in order to approximate the solution at suitable future time levels. Second, a holomorphic recovery procedure is carried out, providing the required approximations for the preceding times. The analysis is valid in the maximum-norm setting, and rigorous estimates are derived. Among other advantages, the method can also be applied to nonlinear problems, and it produces a continuous output. Some numerical illustrations are presented.Key words. ill posed problems, backward parabolic problems, maximum-norm, holomorphic recovery, harmonic measure, Chebyshev nodes, least squares method AMS subject classifications. 65J10, 65J20, 65M15, 65M20, 65M30
PII. S00361429013864221. Introduction. The present paper is devoted to introducing and analyzing a new numerical method for backward parabolic problems. Our main estimate relies on an assumption (see (2.7) in section 2) that, for standard discretizations of classical parabolic problems, holds only in the maximum-norm setting. However, in order to outline the main difficulties associated with the kind of ill-posed problems we have in mind, let us start by adopting an abstract point of view. Thus, let X be a complex Banach space and let A : D(A) ⊂ X → X be the infinitesimal generator of a holomorphic semigroup S(t), t ≥ 0, of linear and bounded operators in X. We do not assume that A is densely defined so that S(t) might fail to be continuous at t = 0 (see, e.g., [48]). In particular, this allows us to consider diffusion problems in the context of X = L ∞ . It is well known that the forward Cauchy problem