Díaz Díaz, Jesús Ildefonso2023-06-202023-06-201991-03-280764-4442https://hdl.handle.net/20.500.14352/57511We show how the approximate controllability of nonlinear parabolic problems may fail although it is a well-known property for linear equations. For the case of the obstacle problem the answer depends on the negativeness of the righ hand side term and for semilinear equations it depends on the sub or superlinear character at the infinity of the nonlinear term.frajournal articlehttp://cat.inist.fr/?aModele=afficheN&cpsidt=19661531restricted access517.911.7approximate controllabilitynonlinear parabolic problemsobstacle problemEcuaciones diferenciales1202.07 Ecuaciones en Diferencias