Dear all, I try to extract the values of a function h, at some specific positions with the function .at() . I define a coarse mesh with Nx_fine = int(Lx/0.4) + 1 Ny_fine = int(Ly/0.4) + 1 coarse_mesh = RectangleMesh(Nx_coarse,Ny_coarse,Lx,Ly,quadrilateral=True) coarse_V = FunctionSpace(coarse_mesh, "CG", 1) coarse_h = Function(coarse_V, name="h") V_vec_c = VectorFunctionSpace(coarse_mesh, "CG", 1) coarse_points = Function(V_vec_c , name="coarse_points") coarse_points.interpolate(SpatialCoordinate(coarse_mesh)) Then I define a finer mesh with Nx_fine = int(Lx/0.1) + 1 Ny_fine = int(Ly/0.1) + 1 fine_mesh = RectangleMesh(Nx_fine,Ny_fine,Lx,Ly,quadrilateral=True) fine_V = FunctionSpace(fine_mesh, "CG", 1) fine_h = Function(fine_V, name="h") Then I load an h5 function into fine_h (defined on the same function space) with dumb_file_fine = DumbCheckpoint(save_path+"fine/h_0", mode=FILE_READ) dumb_file_fine.load(fine_h) dumb_file_fine.close() But then, when I try to extract the values of fine_h at the coordinates of coarse_mesh with coarse_data_fine = fine_h.at(coarse_points.dat.data_ro) I get this error: [0]PETSC ERROR: ------------------------------------------------------------------------ [0]PETSC ERROR: Caught signal number 11 SEGV: Segmentation Violation, probably memory access out of range [0]PETSC ERROR: Try option -start_in_debugger or -on_error_attach_debugger [0]PETSC ERROR: or see http://www.mcs.anl.gov/petsc/documentation/faq.html#valgrind [0]PETSC ERROR: or try http://valgrind.org on GNU/linux and Apple Mac OS X to find memory corruption errors [0]PETSC ERROR: configure using --with-debugging=yes, recompile, link, and run [0]PETSC ERROR: to get more information on the crash. -------------------------------------------------------------------------- MPI_ABORT was invoked on rank 0 in communicator MPI_COMM_WORLD with errorcode 59. NOTE: invoking MPI_ABORT causes Open MPI to kill all MPI processes. You may or may not see output from other processes, depending on exactly when Open MPI kills them. -------------------------------------------------------------------------- Is someone familiar with this error ? Thanks, Floriane