Using a classical finite volume piecewise constant approximation of the sol
ution of an elliptic problem in a domain Omega, we build here an approximat
e gradient of the solution. It is then shown that this approximate gradient
converges in H-div(Omega). An error estimate is given when the solution be
longs to H-2(Omega). (C) 2001 IMACS. Published by Elsevier Science B.V. All
rights reserved.