When using one of the blocks of sublibrary Noise, on the same or a higher hierarchical level, Noise.GlobalSeed must be dragged resulting in a declaration

inner Modelica.Blocks.Noise.GlobalSeed globalSeed;

The GlobalSeed block provides global options for all Noise blocks of the same or a lower hierarchical level. The following options can be selected:

Icon Description
useAutomaticSeed=false (= default):
A fixed global seed is defined with Integer parameter fixedSeed. The value of fixedSeed is displayed in the icon. By default all Noise blocks use fixedSeed for initialization of their pseudo random number generators, in combination with a local seed defined for every instance separately. Therefore, whenever a simulation is performed with the same fixedSeed exactly the same noise is generated in all instances of the Noise blocks (provided the settings of these blocks are not changed as well).
This option can be used (a) to design a control system (e.g. by parameter optimization) and keep the same noise for all simulations, or (b) perform Monte Carlo Simulations where fixedSeed is changed from the environment for every simulation, in order to produce different noise at every simulation run.
An automatic global seed is computed by using the ID of the process in which the simulation takes place and the current local time. As a result, the global seed is changed automatically for every new simulation, including parallelized simulation runs. This option can be used to perform Monte Carlo Simulations with minimal effort (just performing many simulation runs) where every simulation run uses a different noise.
The noise in all Noise instances is switched off and the blocks output a constant signal all the time (usually zero). This option is useful, if a model shall be tested without noise and the noise shall be quickly turned off or on.

Additionally, the globalSeed instance calls function initializeImpureRandom to initialize the impure random number generators (impureRandom and impureRandomInteger). The return value of this function is stored in parameter id_impure. Whenever one of the impure random number generators need to be called, "globalSeed.id_impure" has to be given as input argument.

Note, the usage of this block is demonstrated with examples AutomaticSeed and ImpureGenerator.

Please note that only one globalSeed instance may be defined in the model due to the initialization of the impure random number generators with initializeImpureRandom! So, the block will usually reside on the top level of the model.


Date Description
June 22, 2015
DLR logo Initial version implemented by A. Klöckner, F. v.d. Linden, D. Zimmer, M. Otter.
DLR Institute of System Dynamics and Control

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