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Determining Actual Simulation Time

Question asked by dbengtson on May 1, 2007
Latest reply on May 3, 2007 by kkladopoulos

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Hi:

I'm running a Ptolemy sim, and I've got a question about the actual simulation time. With multiple time sinks in a simulation, it's possible for the simulation to run longer in the simulation domain environment than the default time stop. Is there a way to determine the actual simulation time length?

Thanks

Dave

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kkladopoulos May 1, 2007 12:29 PM
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I am sorry but I do not quite understand your question. The DefaultTimeStart and DefaultTimeStop are just two global variables that are defined for you in case you want all your sinks to collect data over the same time period. Each sink has its own Start and Stop parameters that are by default set to DefaultTimeStart and DefaultTimeStop but can be set to any value.

The simulation will run until all the sinks have collected the data they were set to collect.
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dbengtson May 2, 2007 12:24 AM
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Hi:

I understand that the various sinks will collect data until they are full. However, since this overrides the default time start/time stop. For example, your simulation could have a default time stop of 1 mSec, but the simulation could run for 3 mSec, if there is a sink that needs more data. The sinks that are full at 1 mSec will only show that 1 mSec of data, and the other sinks will show the data that they collect as well, which might not be explicitly time indexed, like a BER or EVM block. Is this clearer?

Dave
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kkladopoulos May 2, 2007 5:27 AM
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Thanks for the clarification.

A BER sink has a Stop parameter as well and can be used to collect data from Start to Stop. However, the BER sink is a lot more useful in the Estimation Relative Variance mode, where the model collects as much data as needed to achieve a statistically meaningful BER estimate. In this case, you do not know a priori how long the simulation will run (Stop is used only as an upper bound just in case the Estimation Relative Variance is not met).

EVM sink has a SymTime and SymBurstLength parameters. Stop is effectively equal to Start+SymTime*SymBurstLength.

I also want to clarify again that DefaultTimeStart and DefaultTimeStop are not the default simulation time start and stop. The simulation time start is always 0. The simulation time stop depends on how the sinks are set up. DefaultTimeStart and DefaultTimeStop are just two global variables that are defined for you in case you want all your sinks that have Start=DefaulTimeStart and Stop=DefaultTimeStop to collect data over the same time period.
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dbengtson May 3, 2007 1:25 AM
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Hi:

So with a BER test, how would I determine how long the simulation domain run time was?

On a related note, how would i set up a time sink to collect data as long as the simulation ran? It seems that setting default time starts and default time stop's are not quite what i want to do.

Thanks

Dave
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kkladopoulos May 3, 2007 6:04 AM
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When the BER sink runs in the Start to Stop mode (that is when EstRelVariance is 0) the sink will collect data up to Stop.

When the BER sink runs in the Estimation Relative Variance mode (that is when EstRelVariance is greater than 0) the sink will collect as much data needed to satisfy the variance. When this happens before Stop is reached the sink prints a message in the status window saying how many symbols it processed. You can multiply that number with the symbol time and add Start to it to find how long the simulation ran.

Alternatively, you can set the sink to write the BER value every N number of symbols processed (set berOutput to ber vs time every NNN symbols). In this case, you get a variable (in the dataset) called BER, which is the BER curve versus time. The timestamp of the last value recorded is the simulation time.

To answer your second question, set ControlSimulation parameter to NO. In this case, the sink will collect data starting from Start and until the simulation finishes (of course, in this case there must be some other sink that controls the simulation).
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Determining Actual Simulation Time

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