Add missing siteinds and mpo method

Author: mtfishman

src/sitetype.jl

@@ -20,6 +20,11 @@ function siteinds(x, g::AbstractGraph; kwargs...)
   return siteinds(to_siteinds_callable(x), g; kwargs...)
 end
 
+# Convenient syntax for path graph.
+function siteinds(x, nv::Int; kwargs...)
+  return siteinds(x, path_graph(nv); kwargs...)
+end
+
 function to_siteind(x, vertex; kwargs...)
   return [siteind(x, vertex_tag(vertex); kwargs...)]
 end

src/treetensornetworks/opsum_to_ttn/opsum_to_ttn.jl

@@ -649,6 +649,10 @@ end
 function mpo(os::OpSum, external_inds::Vector; kwargs...)
   return ttn(os, path_indsnetwork(external_inds); kwargs...)
 end
+function mpo(os::OpSum, s::IndsNetwork; kwargs...)
+  # TODO: Check it is a path graph.
+  return ttn(os, s; kwargs...)
+end
 
 # Conversion from other formats
 function ttn(o::Op, s::IndsNetwork; kwargs...)