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10.5 Manipulation of Normal Modes

There are several commands that con modify the normal mode vector space. In addition to the obvious ones such as READ NORMal-modes and DIAGonalize, there is also an EDIT command which can be used to modify the normal mode data structure. The EDIT DELETE command will delete specified modes from the date structure. The EDIT ORTHogonalize command is used to orthogonalize and optionally normalize a particular subset of normal modes. Additional modes can be added three at a time with the EDIT INCLude TRANslation and EDIT INCLude ROTAtion commands. These commands will add on the translation and rotation eigenvectors respectively. This option is important when individual Coreolis coupling terms are needed. Single additional modes may be added with the EDIT INCLude COMP or the EDIT INCLude FORCe or the EDIT INCLude USER commands. For the COMP option, the difference between the comparison and main coordinate sets will be appended, for the FORCe option, the current values in the force arrays (from the last energy evaluation) will be appended. There is also the ability to specify a user vector. this is done by the inclusion of the subroutine USERNM in your USERSB and using the USERLINK facility, see CONGEN Modifications. For all of the EDIT INCLude options, the defaults are to mass weight, normalize, and orthogonalize to the rest of the vector space. To skip any of these steps, the NOMA, NONO, and NOOR keywords must be specified.

There are two commands which are used to obtain information about particular normal modes without modifications. These are the PRINT NORMal-modes and PROJect subcommands. The PROJect command will project one of; FORCe (the current force), COMParison (the difference between the main coordinates and the comparison set), and USER (a user supplied mode or coordinate displacement). The information displayed is:

     MODE integer    - mode number
     FREQUENCY       - frequency of this mode
     NORMAL DOTPR    - actual dotproduct of normalized vectors
     PROJECTION      - ratio of guess vector projection to step length
     APPROX DEL E    - estimate of energy increase along this mode
     TYPE            - type of step (FACT, RMS, KCAL, TEMP)
     STEP            - step length for this step type

The NOMAss and NONOrm keywords may be used to prevent mass weighting or normalization of modes.

The comparison coordinates can be modified with the FILL COMP command. This command will copy the main coordinate set to the comparison set, and then step along the specified mode by the specified magnitude. When the append (APPE keyword) is used, the main coordinates are not first copied. The FILL NORM command will fill the normal mode coordinate displacement arrays with the specified vector. Again, the append option will prevent the zeroing of these arrays before stepping along the mode. Several other commands use and modify the normal coordinate displacement vectors, so the FILL NORM command should be executed just before exiting to CONGEN with the END command.