..where we discuss density operators wrt SymPy

Month: June, 2012

Week 5 : Tr class implementation

I had not blogged during last week since I was away at the summer school where I had an opportunity to listen to and talk to both physicists and cs theorists working on the next quantum computer! There were  great presentations and the videos should be available shortly. So, now back to Sympy!

Tasks accomplished this week

My main tasks for this week was to address all comments on pending PR 1333. In addition I had planned to complete printing operations on Tr operator and get started with qubit related Tr operations.  I accomplished the task on addressing comments on PR 1333 and also completed basic printing operations along with having the notebook examples done.  The changes outside of PR 1333 are available in my githhub branch(trace_permute_equal) and I plan to submit a PR for these changes as soon as PR 1333 is merged.

In addition I worked on providing a permute() function and also had to play around with implementation of overriding _hashable_contents() method.  I had spend some time in figuring out the details of such an implementation and there was some discussion on this on the mailing list.  For now, I have these 2 functions implemented ( but commented out) in branch trace_permute_equal.

Therefore, one task that remained but which I could not get to this week was qubit implementation related to Tr.  Also, currently I am in the process of writing up how Tr operations should work on TensorProducts. I should have a write up very soon.

The tasks for next week, therefore would be  (roughly in this order)

1. Share a write up on TensorProduct wrt to Tr operations.

2. Push qubit related changes to my git repo

3. Get started on TensorProduct/Tr and have the first cut ready for review.

4 Get PR 1333 merged.

5. Get branch trace_permute_equal merged. This branch has minor changes and I hope to get this merged as well this week.

Happy coding!

Week 3: Activity Summary

My week started with some design discussion with my mentors @ellisonbg and @flacjacket.  We had a preliminary discussion on how we should go about implementing the Tr (trace) operator.

Based on the preliminary discussion, I submitted a PR 1333 purely for review and got some useful comments. I went back to work and addressed almost all the comments/suggested provided and I have updated the PR with my new changes.

As it stands now, the current PR 1333 has the basic functionality needed for Tr operation. This version still does not handle reduced trace operations and also does not use any options passed through **kwargs.  Even, printing will have to be fixed. But, barring any major issues after few more iterations the coming week I am confident this PR can be merged.

So, assuming I will not be adding any more features to the PR, my plan for next week is make sure this PR gets accepted.  Since, I am at the summer school next week, I may not be doing any other new coding activity. So, my minimal goal is to make sure this PR is merged by end of next week.

I plan to branch out of this PR, to work on the following activities during next 2 weeks(mostly week after):

1. Fix printing for Tr operator. Currently, the printing is pretty crude. I will also add examples for Notebook along with this task.

2. Fix the is_number operation ( based on what suggestions I get). I am still to understand what “is_number” means to sympy and what scenarios Tr needs to handle.  I need to work on this property, since this property is called from the base classes for when 2 Tr objects are added through Add(*[Tr(args,indices)]) operation.

3. Integrate currently existing Qubit logic for partial trace operation.

The above 3 tasks should go into the next PR.

4. Meanwhile, I would like to chat with my mentors and about all use cases (general/special) that we will have to address to TensorProducts wrt to density operators and eventually partial trace operations.

Edit 1: Update (1) to include Notebook.

Week 2: Activity Summary

This week there was fewer lines of code than last week. But, with this week I have almost(except partial trace) merged all changes from @ellisonbg’s densityop branch and ready to extend the implementation to incorporate other features.  Most of the time I spent this week is to review and structure my work for the coming weeks and address comments on previous PR . I have provided a detailed plan below.

Tasks performed this week

1.  Responded to and completed all comments on last weeks pull PR1312.
2.  Pushed a minor code change branch to my git account. This change handles entropy for general density operators.  (I am still waiting for the previous pull request to get merged, since this pull request was branched off that.)
3.  Review and understand the partial trace operations and qubit related implementation.  Further notes will be prepared for the discussion.
4. Understand current implementation of tensor products to plan work for coming weeks.

My plan for weeks 3,4,5,6 ( based on design discussion we have had regarding partial trace )

(Note, the detailed plan here still meets the timeline outlined in the proposal. The only change is I will be working fewer hours during Week 4(June 10-16), since I am at the summer school. Hopefully, I can contain the work to not flow into later weeks). 

Week 3/4

Implement/test partial trace methods [ _eval_partial_trace ] and other required methods for following classes:

QubitDensity (name suggestion needed!) : for this I will use the current bit-twiddling algorithm but add detailed test cases.
TensorProduct : Code to handle density operators ( both qubit based, and generic) during expand, mul operations.
TensorProduct : _eval_partial_trace method will split the sub-system to trace. and then based on states inside Tr(|i><k|).  [ This needs more discussions during the next few days and during IRC session.]
Sub-classes of ‘State’ : Need to decide which subclasses need and how it should be done.

Week 5

Symbolic Trace operations and Partial Trace operations.

Week 6

Changes to qapply for L and R operations and any operations that would be needed based on changes so far. (will also fix the bug identified in PR 1312)

Other related learning activities this week.

I tried IPython Notebook and I absolutely love it. Now, I am using that as my command line interface for running sympy commands and understanding current implementation.  The best thing Notebook has done to my workflow is help me save my scratch work and go back whenever I need it. Thanks @ellisonbg.

I did have to jump some hoops to set up Notebook on Ubuntu 11.04, since I had to build a lot of dependencies myself. I plan to blog about it as part of another post.  A minor pain point with it is, I need to drag/drop files I want to work on. Wish it gave me an option to type in the URL to a saved notebook rather than forcing me to open a FileManager window to find file to drag and drop.