An Almost L-Stable BDF-type Method for the Numerical Solution of Stiff ODEs Arising from the Method of Lines Higinio Ramos, Jesús Vigo-Aguiar Scientific Computing Group, Facultad de Ciencias, Universidad de Salamanca, Spain Received 1 March 2006; accepted 10 March 2006 Published online 12 February 2007 in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/num.20212 A new BDF-type scheme is proposed for the numerical integration of the system of ordinary differential equations that arises in the Method of Lines solution of time-dependent partial differential equations. This system is usually stiff, so it is desirable for the numerical method to solve it to have good properties concern- ing stability. The method proposed in this article is almost L-stable and of algebraic order three. Numerical experiments illustrate the performance of the new method on different stiff systems of ODEs after discretiz- ing in the space variable some PDE problems. © 2007 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 23: 1110–1121, 2007 Keywords: BDF-type methods; stiff initial-value problems; A(α)-stability; almost L-stability; Method of Lines INTRODUCTION In this article we consider a new numerical method for solving time-dependent partial differential equations of the form ∂u ∂t = ∂x r ( x , t , u, ∂u ∂x ) + f ( x , t , u, ∂u ∂x ) , (x , t) ∈[a, b]×[t 0 , t f ], (1) with Dirichtlet boundary conditions given by u(a, t) = 1 (t), u(b, t) = 2 (t), t ∈[t 0 , t f ] (2) and initial condition given as u(x , t 0 ) = φ(x), x ∈[a, b]. (3) Correspondence to: Higinio Ramos, Scientific Computing Group, Facultad de Ciencias, Universidad de Salamanca, Salamanca 37008, Spain (e-mail: higra@usal.es) Contract grant sponsor: JCYL; contract grant number: SA 024/04 Contract grant sponsor: CYT; contract grant number: BMF 2004-295 © 2007 Wiley Periodicals, Inc.