Help with type instabilities

General Usage
8

Hey thanks for the reply. I had indeed looked at TensorOperations, but I do need everything in 2D matrix form. I improved the code further (with some help) and managed to get the partial trace even faster:

julia> using Schrodinger, BenchmarkTools
julia> A = rand(36,36); out = (2,); sysdims = (2,9,2);
julia> @benchmark ptrace($A,$out,$sysdims)
BenchmarkTools.Trial:
  memory estimate:  480 bytes
  allocs estimate:  5
  --------------
  minimum time:     1.275 μs (0.00% GC)
  median time:      1.431 μs (0.00% GC)
  mean time:        1.520 μs (2.17% GC)
  maximum time:     181.442 μs (97.48% GC)
  --------------
  samples:          10000
  evals/sample:     10

The code is now available here (the package itself is not fully ready for prime time) for those interested.