Define svd

[mtfishman]

Followup to ITensor/TensorAlgebra.jl#20.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 33 lines in your changes missing coverage. Please review.

Project coverage is 32.68%. Comparing base (eab2fec) to head (c261918).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/tensoralgebra.jl	0.00%	33 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #20      +/-   ##
==========================================
- Coverage   34.01%   32.68%   -1.34%     
==========================================
  Files          14       14              
  Lines         638      664      +26     
==========================================
  Hits          217      217              
- Misses        421      447      +26     

Flag	Coverage Δ
docs	32.57% <0.00%> (-1.33%)	⬇️

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[mtfishman]

@lkdvos this is meant as a starting point, we'll need to add truncation, check that it works with block sparse arrays (now that ITensor/BlockSparseArrays.jl#16 is merged), etc. Part of my reason for rushing this a bit is so that I can test out some ITensorMPS.jl code that makes use of SVD. Also I think it is good to have a starting point in place to work with, even if we don't get all of the corner cases handled right now.