Stop Conditions (STOP)

The optimization is stopped when certain criteria are fulfilled. These criteria are defined with the STOP command.

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STOP

A stop condition is defined by assigning a logical variable (LOGICAL) to an optimization task (OPTIMIZE). The stop condition can be specifically addressed with its user-defined name (ID_NAME).


STOP
 ID_NAME  = stop_name
 LOGICAL  = logical_name
 OPTIMIZE = opt_grp_name
END_

The stop condition ends the optimization for the selected optimization group when the value for the assigned logical variable is TRUE. If several STOP conditions have been defined for an optimization group, the optimization for this group is ended when one of the stop conditions is fulfilled (corresponds to a logical OR condition).

The logical variable can vary significantly. Before using the STOP command, numerical and logical variables must be defined with the VARIABLE and LOGICAL commands.

The flexibility is achieved using various logical variables as the stop criteria. Logical operations AND or OR can also be included in the STOP command by defining the logical variables.

For shape optimization, typical stop conditions can be defined more directly by an enhanced stop command: 


STOP
 ID_NAME  = stop_command
 MOD_NDGR = all_nodes
 MOD_TYPE = MAX, CTRL_INP_SHAPE
 MOD_OPER = LE
 MOD_REF  = 0.01, MULT, FIRST
 OPTIMIZE = run
END_

In this case, the optimization task "run" should stop when the maximum equivalent stress (CTRL_INP_SHAPE) of the node group all_nodes is smaller than 1% of the maximum equivalent stress of the first iteration.

Using this enhanced stop command, the extraction of variables and their logical comparison is performed internally by Tosca Structure and need no longer be specified manually by the user. For a detailed description of the several items, refer to the commands manual.

If required, the global upper limit for the maximum number of iterations can be set with a separate, brief command. In this case, a definition of logical variables is not required.


STOP
 ID_NAME  = STOP_CONDITION
 ITER_MAX = <value>
END_

A global stop condition is integrated in the system to limit the maximum number of iterations for safety reasons. This stop condition is always active. The default value for the maximum number of iterations is set to 40. As an example, the command


STOP
 ID_NAME  = STOP_CONDITION
 ITER_MAX = 55
END_

increases the maximum number of iterations.

Important:

When the optimization is halted because of a stop condition, it is possible that the required results are not achieved. This is especially true for topological optimization when stipulating the global tensile stiffness.