Julia is very slow compared to python/numpy. What am I doing wrong here?

General Usage Performance
,
2

I assume Qutip uses sparse arrays. You can do the same in Julia (like you - I have not tried to optimize code - just added sparse):

julia> using SparseArrays

julia> function ψtest(K)
           if K > 1 && K % 1 == 0
               return kron(ψtest(K-1), sparse([-1. 0.;0. 1.]))
           elseif K == 1
               return 1/√(2) * sparse([0. 1.;1. 0.])
           end
       end
ψtest (generic function with 1 method)

julia> @time ψtest(16);
  0.002063 seconds (182 allocations: 3.012 MiB)

julia> @time ψtest(25);
  1.169190 seconds (290 allocations: 1.500 GiB, 17.61% gc time)

with dense matrix K=25 for sure will not fit in your RAM.

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