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 Dear Wen, If you really need to compute the divergence operator (it is rare to really have to compute it, except for intance for residual a posteriori estimators) you can use compute_hessian in getfem_derivatives.h, yes. The derivatives are stored in Fortran order (\partial^2 u / \partial_1 \partial_1, \partial^2 u / \partial_1 \partial_2, ... \partial^2 u / \partial_1 \partial_N, \partial^2 u / \partial_2 \partial_1) on each finite element node on the finite element method it is interpolated and gathered on the whole vector (i.e. derivative on the first dof, then derivatives on the second dof, and so on). Yves. Le 12/12/2013 16:46, Wen Jiang a écrit : Dear all, I am wondering how to calculate the divergence of strain tensor in linear elasticity problem. It involves calculating the second derivatives which could be extracted from the compute_hessian in getfem_derivatives.h. Is there any existing function to get the divergence directly? If not, could anyone tell me what is the order that the derivatives are stored in compute_hessian function? Thanks. Regards, Wen _______________________________________________ Getfem-users mailing list address@hidden https://mail.gna.org/listinfo/getfem-users  -- Yves Renard (address@hidden) tel : (33) 04.72.43.87.08 Pole de Mathematiques, INSA-Lyon fax : (33) 04.72.43.85.29 20, rue Albert Einstein 69621 Villeurbanne Cedex, FRANCE http://math.univ-lyon1.fr/~renard ---------