denseblocks on dense tensor fails

ITensor Julia Questions
1

denseblocks(A) where A is a dense tensor crashes.
This is a funny end case, but I would simply expect it to return A.

using ITensors, ITensorMPS

for conserve_qns in [true, false]
    i = siteind("S=1"; conserve_qns)
    o = op(i,"Sz") # diagonal matrix in dense format
    S = svd(o,i).S # diagonal matrix in diag format
    denseblocks(S) # works 
    denseblocks(o) # fails if conserve_qns==false
end

For context, I ran into this in generic code where I want to initialize a Krylov run with some diagonal matrix, with or without quantum numbers. As adding diagonal matrices is not supported, I use denseblocks to convert the input to a dense (block) matrix. But if the input was already in dense format and without quantum numbers then denseblocks fails.

2

Thanks for the report, that should definitely work. We’ll look into it.

3

@matanlotem could you raise an issue in the ITensors.jl repository (GitHub · Where software is built) about this, including the error message? It is easier to track it that way.