[Pw_forum] how to do optimization with the lattice parameters in-plane being fixed

[朱林光]

Dear all qe users:
 Im a new user to qe,and i want to do some optimizations on tetragonal phase PbTiO3 with constraints in-plane to study the phase transition under different epitaxial  strain ,but i dont know how to do optimization with the lattice parameters in-plane being fixed and all atoms  the lattice parameter out-of-plane being relaxed in qe. Can anyone help me?