3D visualization in Acumen

Anita and Yingfu continue to work on a paper describing 3D visualization for Acumen, Acumen3D. The problem formulation is along the lines of "what would be a good core language for 3D animation?" The paper will highlight some interesting features of Acumen3D, such as directly linking simulation variables to visualization objects, and dynamically generating objects. Yingfu is currently at Rice University but he and Anita will continue to work together on the paper.

Collaborating with PSU

Anita is planning a visit to Portland State University (PSU) in September to discuss possible collaboration projects. The collaboration between Halmstad University (HU) and PSU started a few years ago with Dan Hammerstrom as a guest researcher at HU. In order to strengthen the ties between both universities, a joint project was formulated. The initial idea was to use Acumen to model electric vehicle and smart grid components in Dan's electric vehicles course at PSU. After Dan moved to DARPA, he suggested Robert Bass be HU's link to PSU. Anita, Veronica, Dan and Robert had a Skype meeting at the beginning of August, and it was decided that Anita would pay a short visit to Robert at PSU to discuss the continuation of the project.

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Anita Pinheiro Sant'Anna
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Intelligent Systems Lab
Halmstad University
+46 35167849

Unit test for symbolic differentiation

This week Yingfu started developing unit test cases for the symbolic differentiation implementation in Acumen.  Some examples are shown below:

dif("2*x^2","x")  should be (parseExpr("4*x"))

dif("cos(x)","x")  should be (parseExpr("-sin(x)"))

dif("x^2/(x+1)","x") should be (parseExpr("(2*x*(x+1)-x^2)/(x+1)^2"))

dif("x^x","x") should be (parseExpr("x^x*(log(x)+1)"))

Coming work will include the old property-based test cases.  Anita and Yingfu continued working on the paper about Acumen3D and built a comparison table with other simulation tools including LabView, Simulink and Modelica. 

Property-based testing of intervals and interval functions

This week Adam and Jan started developing a property-based test suite for the enclosure-based solver that is under development. The properties aim to meet two goals, first to catch bugs in the implementation, and second to make up an automatically testable specification of the implementation. Pure Scalacheck properties were chosen over properties expressed in a ScalaTest style, because they give more readable output when used in conjunction with SBT, and seem to give a terser formulation of the properties. So far, properties and generators have been written for intervals and interval functions.

Event-variable independence analysis

During last week Jan has been working on an implementation of an event-variable independence analysis for the hybrid solver under development. The analysis determines when it is safe to ignore events when building an enclosure of all possible trajectories for a hybrid IVP over a fixed time segment. The analysis uses equality of IVP fields and reset maps and to facilitate such judgements these functions have been represented essentially as syntax trees. The representation makes it simple to e.g. test when tow fields have the same effect on a given variable, or when a reset map acts as the identity on the variables a given variable depends. Coming work will focus on testing the solver in preparation of integration with the Acumen code base.

Toward symbolic differentiation in Acumen

This week Adam and Yingfu have been working on integrating the
symbolic differentiation implementation with Acumen. This amounted to
adding a code transformation step which applies the previously
developed logic, updated to operate on the Acumen AST types. This
approach was chosen over one where a specialized AST is used, as the
existing types did not add much syntactic overhead. Future work in
this area includes adding support for more language constructs and
improving the handling of singularities.

Yingfu deposits Masters thesis

Yingfu has completed and deposited his masters thesis at Halmstad University.  The title of his thesis is "Lightweight Three-Dimensional Visualization for Hybrid Systems Simulation."  The basic idea behind the thesis is to find an easy way to give engineers access to some of the most basic functionality provided by OpenGL in a way that can help them during the process of modeling and simulation of cyber-physical systems.  In the propose approach, all the user needs to do is to define the value of some special variables, and they are automatically used to generate an 3D animation based on the results of the simulation.  The thesis, defense presentation, and all related Acumen models can be found in online archive available from the group website.  Yingfu and Anita are working on writing up the results as a conference submission.