This paper proposes a partially inexact alternating direction method of multipliers for computing approximate solution of a linearly constrained convex optimization problem. This method allows its first subproblem to be solved inexactly using a relative approximate criterion, whereas a proximal term is added to its second subproblem in order to simplify it. A stepsize parameter is included in the updating rule of the Lagrangian multiplier to improve its computational performance. Pointwise and ergodic interation-complexity bounds for the proposed method are established. To the best of our knowledge, this is the first time that complexity results for an inexact ADMM with relative error criteria has been analyzed. Some preliminary numerical experiments are reported to illustrate the advantages of the new method.2000 Mathematics Subject Classification: 47H05, 49M27, 90C25, 90C60, 65K10. and jefferson@ufg.br). The work of these authors was supported in part by CAPES, CNPq Grants 302666/2017-6 and 406975/2016-7.2) to provide pointwise and ergodic iteration-complexity bounds for the proposed method;3) to illustrate, by means of numerical experiments, the efficiency of the new method for solving some real-life applications.Iteration-complexity results have been considered in the literature for most of exact ADMM variants. Paper [20] presented an ergodic iteration-complexity analysis of the ADMM. Subsequently, [6] and [7] analyzed ergodic and pointwise iteration-complexities of a partially proximal ADMM, respectively. We refer the reader to [21,22,23,24,25,26,27,28] where iteration-complexities of other ADMM variants have been considered. The complexity analyses of the present paper are based on showing that the proposed method falls within the setting of a hybrid proximal extragradient framework whose iteration-complexity bounds were established in [9]. To the best of our knowledge, this work is the first one to present iteration-complexity results for an inexact ADMM with relative error.This paper is organized as follows. Section 2 contains some preliminary results and it is divided into two subsections. The first subsection presents our notation and basic definitions while the second one recalls a modified HPE framework and its basic iteration-complexity results. Section 3 introduces the partially inexact proximal ADMM and establishes its iteration-complexity bounds. Section 4 is devoted to the numerical experiments.
Preliminary ResultsThis section is divided into two subsections. The first one presents our notation and basic results. The second subsection recalls a modified HPE framework and its iteration-complexity bounds.
Notation and Basic DefinitionsThis section presents some definitions, notation and basic results used in this paper.The p−norm (p ≥ 1) and maximum norm of z ∈ R n are denoted, respectively, by z p = ( n i=1 |z i | p )