SU(2) Exact Diagonalization

[qsukhi]

Added a function to compute the low energy eigenstates of a local, SU(2)-symmetric Hamiltonian, in a way that exploits the SU(2) symmetry. Also added some generic SU(2) functionality e.g. functions to compute Clebsch-Gordan coefficients, Fusion Rules, Fusing two indices etc.

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[qsukhi]

@googlebot I signed it!

[mganahl]

thanks @qsukhi I'll take a look!

[mganahl]

Hi @qsukhi, I'm working through the code. It will take me a bit of time since it is a lot of code. In the meantime, can you change indenting to two spaces instead of four? I wonder why the linter didn't catch this.
Also, I noticed that there is a binary file in this PR, is this intentional?

[qsukhi]

Thanks, @mganahl.
-I've reduced the indent to 2 spaces.
-The binary file is a table of factors that come from the Clebsch-Gordan part of SU(2)-symmetric tensor contractions. It is not necessary, as the function Su2ExactDiagonalization() can build the factor tables if the user specifies so (as illustrated in Su2ExactDiagonalization/main.py).

[codecov-io]

Codecov Report

Merging #898 (e1be4b0) into master (523e7a8) will decrease coverage by 0.04%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #898      +/-   ##
==========================================
- Coverage   98.12%   98.08%   -0.05%     
==========================================
  Files         129      129              
  Lines       22790    22257     -533     
==========================================
- Hits        22362    21830     -532     
+ Misses        428      427       -1     

Impacted Files	Coverage Δ
...ornetwork/matrixproductstates/infinite_mps_test.py	84.78% <0.00%> (-1.50%)	⬇️
...ckends/tensorflow/tensorflow_tensornetwork_test.py	59.75% <0.00%> (-1.17%)	⬇️
tensornetwork/linalg/tests/initialization_test.py	84.61% <0.00%> (-0.65%)	⬇️
tensornetwork/backends/decorators_test.py	92.64% <0.00%> (-0.51%)	⬇️
...ensornetwork/tests/tensornetwork_symmetric_test.py	92.70% <0.00%> (-0.37%)	⬇️
tensornetwork/backends/decorators.py	96.77% <0.00%> (-0.20%)	⬇️
tensornetwork/linalg/tests/test_linalg.py	96.31% <0.00%> (-0.20%)	⬇️
tensornetwork/tests/tensor_test.py	98.51% <0.00%> (-0.15%)	⬇️
examples/simple_mera/simple_mera.py	95.49% <0.00%> (-0.12%)	⬇️
...tractors/opt_einsum_paths/path_calculation_test.py	95.74% <0.00%> (-0.09%)	⬇️
... and 44 more

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[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.12%. Comparing base (523e7a8) to head (e1be4b0).
Report is 13 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #898   +/-   ##
=======================================
  Coverage   98.12%   98.12%           
=======================================
  Files         129      129           
  Lines       22790    22790           
=======================================
  Hits        22362    22362           
  Misses        428      428           

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