Add DiagonalTensorMap(::AbstractTensorMap)

Author: lkdvos

src/tensors/diagonal.jl

@@ -73,6 +73,16 @@ end
 TensorMap(d::DiagonalTensorMap) = copy!(similar(d), d)
 Base.convert(::Type{TensorMap}, d::DiagonalTensorMap) = TensorMap(d)
 
+# similar to Diagonal: simply take diagonal
+function DiagonalTensorMap(t::AbstractTensorMap)
+    numin(t) == numout(t) == 1 && domain(t) == codomain(t) || throw(SpaceMismatch())
+    d = DiagonalTensorMap{scalartype(t)}(undef, space(t, 1))
+    for (c, b) in blocks(t)
+        copy!(block(d, c), Diagonal(b))
+    end
+    return d
+end
+
 function Base.convert(::Type{DiagonalTensorMap{T,S,A}},
                       d::DiagonalTensorMap{T,S,A}) where {T,S,A}
     return d