GSoC Week 4

17 Jun 2016

I started off this week writing the example code for a pendulum defined by x and y coordinates instead of an angle, theta. This was to show how the eombase.EOM class would handle a differential algebraic system. I also altered the simple pendulum example I made early on in the project to show how it would look as an eombase.EOM example. Of the examples I have made for the base class this one stands out as currently being the only one making use of the equations of motion generators (the other two have the equations of motion entered by hand). While addressing comments on the PR, it was mentioned that a more traditional documentation approach would allow greater visibility of the desired results of the code as the output could be explicitly shown. I agreed and moved all three examples to a single .rst document in PyDy and changed the code to represent the documentation format over example code format. At this point I made a list of all of the attributes and methods I though the base class should represent and made sure they were represented in the example documentation. In addition I included multiple ways I thought error messages should be brought up for incorrect uses of the base class. This information is currently awaiting review.

In addition to the work on the base class I had to fix the kane benchmark I made early on in the project. At some point in the last few months the input order for kane.kanes_equations() was flipped and this caused the benchmark to not be able to run on pervious versions of Sympy. My fix was to use a try/except clause to catch the error produced by the older versions of Sympy and alter the input order based on whether or not the error was produced. This code sits at PR #29 and it too is awaiting review/approval.

While I have been waiting for review of the base class PR, I have begun reading through Roy Featherstone’s book, “Rigid Body Dynamics Algorithms”. I have spent time going through Jason’s overhaul of KanesMethod as well and trying to provide as much useful feedback as I can.

Lastly I reviewed PR #11209 this week. The PR correctly alters code that tests for the presence of a key in a dictionary. It also altered the indentation of the code that immediately followed. I eventually came to the conclusion that this was a correct alteration because the variable eq_no is set in the dictionary key test and is used in the code that follows the test. I commented that the PR looks good to me and another member of SymPy merged it. This makes me slightly worried that too much value may be attached to my opinion as I still feel like a beginner.

Future Directions

I will continue reading through Featherstone’s book until I recieve feedback on the proposed base class API at which time I will address the reviewer’s comments and hopefully begin work on the base class itself.

PR’s and Issues

  • (Open) Improved the explanation of the 5 equations in the Kane’s Method docs PR #11183
  • (Open) Created a basis on which to discuss EOM class PR #353
  • (Open) Minor fix in KanesMethod’s docstring PR #11186
  • (Open) Fixed kane benchmark for different input order PR #29
  • (Merged) Fix issue #8193 PR #11209

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