.AixLib.Fluid.Examples.Performance.Example6

Information

This example, together with AixLib.Fluid.Examples.Performance.Example7, illustrates the overhead generated by divisions by parameters. See Jorissen et al. (2015) for a complementary discussion.

Running the following commands allows comparing the CPU times of the two models, disregarding as much as possible the influence of the integrator:

 simulateModel("AixLib.Fluid.Examples.PerformanceExamples.Example6", stopTime=100, numberOfIntervals=1, method="Rkfix4", fixedstepsize=0.001, resultFile="Example6");
 simulateModel("AixLib.Fluid.Examples.PerformanceExamples.Example7", stopTime=100, numberOfIntervals=1, method="Rkfix4", fixedstepsize=0.001, resultFile="Example7");
 

Comparing the CPU times indicates a speed improvement of 56%. This difference almost disappears when adding annotation(Evaluate=true) to R and C.

In dsmodel.c we find:

 DynamicsSection
 W_[2] = divmacro(X_[0]-X_[1],"T[1]-T[2]",DP_[0],"R");
 F_[0] = divmacro(W_[1]-W_[2],"Q_flow[1]-Q_flow[2]",DP_[1],"C");
 

This suggests that the parameter division needs to be handled during each function evaluation, probably causing the increased overhead.

The following command allows comparing the CPU times objectively.

simulateModel("AixLib.Fluid.Examples.Performance.Example6", stopTime=100, numberOfIntervals=1, method="Euler", fixedstepsize=0.001, resultFile="Example6");

See Jorissen et al. (2015) for a discussion.

References

• Filip Jorissen, Michael Wetter and Lieve Helsen.
  Simulation speed analysis and improvements of Modelica models for building energy simulation.
  Submitted: 11th Modelica Conference. Paris, France. Sep. 2015.

Revisions

• April 11, 2016 by Michael Wetter:
  Corrected wrong hyperlink in documentation for issue 450.
• July 14, 2015, by Michael Wetter:
  Revised documentation.
• April 17, 2015, by Filip Jorissen:
  First implementation.