Superconvergence Recovery for the Gradient of the Trilinear Finite Element
For a second-order elliptic boundary value problem in three dimensions, we use an interpolation postprocessing technique to obtain recovered gradients of tri- linear elements over regular meshes. Further, superconvergence of these gradients are proved.
J. H. Liu and D. C. Yin, "Superconvergence Recovery for the Gradient of the Trilinear Finite Element", Advanced Materials Research, Vols. 268-270, pp. 1021-1024, 2011