pretty-printing sparse-Hermitian matrices

[stevengj]

We have specialized display of sparse matrices, but it isn't used when the matrix is wrapped in Hermitian:

For example, this looks nice:

julia> S = sprand(1000,1000,0.0001); S = S + S' + I
1000×1000 SparseMatrixCSC{Float64, Int64} with 1182 stored entries:
⎡⠱⢆⠂⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠘⠀⠀⠠⠀⠀⠀⠀⠠⠐⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⢀⎤
⎢⠈⠀⠑⢄⠀⠀⠀⠀⠀⠀⠀⠁⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠈⠰⠀⠀⠀⠀⠠⠀⠀⠀⎥
⎢⠀⠀⠀⠀⠑⢄⠀⠀⠀⠀⠈⠀⠄⠀⠠⠈⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠂⠀⠀⠀⠈⠀⠀⎥
⎢⠀⠀⠀⠀⠀⠀⠑⢄⠀⠀⠀⠂⠀⠀⠁⢂⠀⡔⠈⠀⠀⠀⠀⠀⠠⠀⠀⠀⠈⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠤⎥
⎢⠀⠀⠀⠀⠀⠀⠀⠀⠕⢅⢀⠀⠀⢐⠀⠠⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠂⢀⠀⎥
⎢⠀⠀⠄⠀⠂⠀⠠⠀⠀⠐⠑⢄⠀⠀⠀⠀⠀⠀⠀⠀⠀⠁⠀⠀⢀⠀⠀⠀⠀⠀⠀⠀⠈⠀⠀⢀⠀⠀⡀⠀⎥
⎢⠀⠀⠀⠀⠀⠁⠀⠀⢀⢀⠀⠀⠑⢄⠄⠀⠀⠀⢀⠀⠠⠂⠀⠀⠀⠀⠀⠁⠀⠂⠠⠀⠀⠀⠀⢀⠄⠈⠀⠀⎥
⎢⣀⠀⠀⠀⡀⠂⠡⢀⠀⡀⠀⠀⠀⠁⠑⢄⠐⠀⠀⠀⠀⠀⠀⠀⢀⠀⠂⠀⠀⠈⠀⠀⠀⠀⠀⠄⠀⠀⠀⠀⎥
⎢⠀⠀⠀⠀⠀⠀⢀⠤⠀⠀⠀⠀⠀⠀⠐⠀⠑⢄⢄⠀⠀⠀⡂⠀⠀⢀⠀⢀⠀⠀⠀⠀⠀⠀⡀⠀⠠⠀⠀⠀⎥
⎢⠀⠂⠀⠀⠀⠀⠂⠀⠀⠀⠀⠀⠀⠐⠀⠀⠀⠑⠑⢄⠀⠀⠀⠀⠀⠀⠠⠀⠀⠀⡀⠄⠀⠠⠀⠀⠀⠀⠀⠀⎥
⎢⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠄⠀⠠⠂⠀⠀⠀⠀⠀⠀⠑⢄⠈⠀⠠⠀⠀⠂⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠐⠀⎥
⎢⠀⡀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠈⠈⠀⠀⠂⠀⠑⢄⠀⠀⠀⠀⠀⠀⠀⠀⠄⠀⠀⠀⠀⠀⠀⠀⎥
⎢⠐⠀⠀⠀⠀⠀⠀⠂⠀⠀⠀⠐⠀⠀⠀⠐⠀⢀⠀⠀⠀⠂⠀⠀⡑⢌⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⎥
⎢⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠄⠀⠈⠀⠀⢀⠀⠂⠠⠀⠀⠀⠀⠀⠑⢄⠀⠀⠀⠀⠀⠁⠈⠠⠀⠈⠀⠀⎥
⎢⠀⠀⠀⠀⠀⠀⠂⠀⠀⠀⠀⠀⠠⠀⡀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠑⢄⠀⠂⠀⠀⠀⠀⠀⠀⡀⠀⎥
⎢⠀⠀⢂⡀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠂⠀⠀⠀⠀⠀⠌⠀⠀⠀⠀⠀⠀⠀⠀⠠⠀⠛⢄⠀⠄⠀⠀⠀⠀⠀⡄⎥
⎢⠀⠀⠀⠀⠠⠀⠀⠀⠀⠀⠂⠀⠀⠀⠀⠀⠀⠀⠀⡀⠀⠀⠀⠁⠀⠀⠄⠀⠀⠀⠀⠄⠑⢄⠄⠠⠀⠀⠀⠀⎥
⎢⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⢀⠀⢀⠀⠄⠀⠈⠀⠀⠀⠀⠀⠀⠀⠀⠂⡀⠀⠀⠀⠀⠀⡁⠑⢄⠀⠀⠀⠀⎥
⎢⠀⠀⠀⠂⡀⠀⠀⠀⠠⠀⠀⠀⡀⠁⠀⠀⠀⠂⠀⠀⠀⠀⠀⠀⠀⠀⡀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠑⢄⠂⠀⎥
⎣⠀⢀⠀⠀⠀⠀⠀⡄⠀⠐⠀⠈⠀⠀⠀⠀⠀⠀⠀⠀⠐⠀⠀⠀⠀⠀⠀⠀⠀⠈⠀⠤⠀⠀⠀⠀⠈⠀⠑⢄⎦

but Hermitian(S) falls back to the generic AbstractMatrix display, which is much less useful:

julia> show(IOContext(stdout, :limit=>true, :displaysize=>(20,80)), "text/plain", Hermitian(S))
1000×1000 Hermitian{Float64, SparseMatrixCSC{Float64, Int64}}:
 1.0   ⋅    ⋅    ⋅    ⋅    ⋅    ⋅    ⋅   …   ⋅    ⋅    ⋅    ⋅    ⋅    ⋅    ⋅ 
  ⋅   1.0   ⋅    ⋅    ⋅    ⋅    ⋅    ⋅       ⋅    ⋅    ⋅    ⋅    ⋅    ⋅    ⋅ 
  ⋅    ⋅   1.0   ⋅    ⋅    ⋅    ⋅    ⋅       ⋅    ⋅    ⋅    ⋅    ⋅    ⋅    ⋅ 
  ⋅    ⋅    ⋅   1.0   ⋅    ⋅    ⋅    ⋅       ⋅    ⋅    ⋅    ⋅    ⋅    ⋅    ⋅ 
  ⋅    ⋅    ⋅    ⋅   1.0   ⋅    ⋅    ⋅       ⋅    ⋅    ⋅    ⋅    ⋅    ⋅    ⋅ 
  ⋅    ⋅    ⋅    ⋅    ⋅   1.0   ⋅    ⋅   …   ⋅    ⋅    ⋅    ⋅    ⋅    ⋅    ⋅ 
  ⋅    ⋅    ⋅    ⋅    ⋅    ⋅   1.0   ⋅       ⋅    ⋅    ⋅    ⋅    ⋅    ⋅    ⋅ 
  ⋅    ⋅    ⋅    ⋅    ⋅    ⋅    ⋅   1.0      ⋅    ⋅    ⋅    ⋅    ⋅    ⋅    ⋅ 
 ⋮                        ⋮              ⋱            ⋮                   
  ⋅    ⋅    ⋅    ⋅    ⋅    ⋅    ⋅    ⋅      1.0   ⋅    ⋅    ⋅    ⋅    ⋅    ⋅ 
  ⋅    ⋅    ⋅    ⋅    ⋅    ⋅    ⋅    ⋅       ⋅   1.0   ⋅    ⋅    ⋅    ⋅    ⋅ 
  ⋅    ⋅    ⋅    ⋅    ⋅    ⋅    ⋅    ⋅   …   ⋅    ⋅   1.0   ⋅    ⋅    ⋅    ⋅ 
  ⋅    ⋅    ⋅    ⋅    ⋅    ⋅    ⋅    ⋅       ⋅    ⋅    ⋅   1.0   ⋅    ⋅    ⋅ 
  ⋅    ⋅    ⋅    ⋅    ⋅    ⋅    ⋅    ⋅       ⋅    ⋅    ⋅    ⋅   1.0   ⋅    ⋅ 
  ⋅    ⋅    ⋅    ⋅    ⋅    ⋅    ⋅    ⋅       ⋅    ⋅    ⋅    ⋅    ⋅   1.0   ⋅ 
  ⋅    ⋅    ⋅    ⋅    ⋅    ⋅    ⋅    ⋅       ⋅    ⋅    ⋅    ⋅    ⋅    ⋅   1.0