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dev:printkey [2020/08/21 10:15] (current) – external edit 127.0.0.1
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 +====== Printkeys ======
  
 +When writing output in cp2k, to the screen or a file, one should use a //printkey//
 +
 +A printkey allows the user to control the output. He can e.g. turn if off, redirect it to a different file, or output after a certain number of iteration (see [[dev:iter_levels]]).
 +
 +To each printkey belongs an input-section, which is always structured in a similar way. For example, the printkey used to write trajectories is controlled by [[http://manual.cp2k.org/trunk/CP2K_INPUT/MOTION/PRINT/TRAJECTORY.html|this input-section]].
 +
 +====== Creating a Printkey Input-section ======
 +
 +<code Fortran>
 + USE cp_output_handling,              ONLY: cp_print_key_section_create
 + !...
 + CALL section_create(subsection,name="print",&
 +      description="Controls the printing properties during an MD run",&
 +      n_keywords=0, n_subsections=1, repeats=.TRUE., required=.FALSE.,error=error)
 + CALL cp_print_key_section_create(print_key,"TRAJECTORY",&
 +      description="Controls the output of the trajectory",&
 +      print_level=low_print_level, common_iter_levels=1,&
 +      filename="",unit_str="angstrom",error=error)
 + CALL section_add_subsection(subsection,print_key,error=error)
 + CALL section_release(print_key,error=error)
 + !...
 +</code>
 +
 +====== Using a Printkey for output ======
 +
 +<code Fortran>
 + USE cp_output_handling,              ONLY: cp_print_key_finished_output,&
 +                                            cp_print_key_unit_nr
 + !...
 + TYPE(cp_logger_type), POINTER :: logger
 + INTEGER                       :: traj_unit
 + !...
 + logger => cp_error_get_logger(error)
 + traj_unit = cp_print_key_unit_nr(logger,root_section,"MOTION%PRINT%TRAJECTORY",error=error)
 + IF (traj_unit > 0) THEN
 +   WRITE(traj_unit, *) "here goes the output"
 + ENDIF
 + CALL cp_print_key_finished_output(traj_unit,logger,root_section,"MOTION%PRINT%TRAJECTORY",error=error)
 +</code>