Parallel vumpssvd

src/algorithms/changebonds/vumpssvd.jl

@@ -77,10 +77,68 @@
     return state, envs
 end
 
+function changebonds_parallel_n(state::InfiniteMPS, H, alg::VUMPSSvdCut,
+                                envs=environments(state, H))
+    #prepare the loops we'll have to run over, this is different depending on wether the length of the state is odd or even ! 
+    subsets = nothing
+    start_locs = nothing
+    if iseven(length(state))
+        subsets = ["even", "odd"]
+        start_locs = Dict("even" => 1:2:length(state), "odd" => 2:2:length(state))
+    else
+        subsets = ["even", "odd", "last"]
+        start_locs = Dict("even" => 1:2:(length(state) - 1),
+                          "odd" => 2:2:(length(state) - 1), "last" => length(state))
+    end
+
+    for subset in subsets
+        new_ALs = copy(state.AL)
+        @sync for loc in start_locs[subset]
+            Threads.@spawn begin
+                @plansor AC2[-1 -2; -3 -4] := state.AC[loc][-1 -2; 1] *
+                                              state.AR[loc + 1][1 -4; -3]
+
+                h_ac2 = ∂∂AC2(loc, state, H, envs)
+                (vals, vecs, _) = eigsolve(h_ac2, AC2, 1, :SR; tol=alg.tol_eigenval,
+                                           ishermitian=false)
+                nAC2 = vecs[1]
+
+                h_c = ∂∂C(loc + 1, state, H, envs)
+                (vals, vecs, _) = eigsolve(h_c, state.CR[loc + 1], 1, :SR;
+                                           tol=alg.tol_eigenval,
+                                           ishermitian=false)
+                nC2 = vecs[1]
+
+                #svd ac2, get new AL1 and S,V ---> AC
+                (AL1, S, V, eps) = tsvd(nAC2; trunc=alg.trscheme, alg=TensorKit.SVD())
+                @plansor AC[-1 -2; -3] := S[-1; 1] * V[1; -3 -2]
+
+                #find AL2 from AC and C as in vumps paper
+                QAC, _ = leftorth(AC; alg=QRpos())
+                QC, _ = leftorth(nC2; alg=QRpos())
+                dom_map = isometry(domain(QC), domain(QAC))
+
+                @plansor AL2[-1 -2; -3] := QAC[-1 -2; 1] * conj(dom_map[2; 1]) *
+                                           conj(QC[-3; 2])
+
+                #make a new state using the updated A's
+                new_ALs[loc] = AL1
+                new_ALs[loc + 1] = AL2
+            end
+        end
+        state = InfiniteMPS(new_ALs; tol=alg.tol_gauge)
+    end
+    return state, envs
+end
+
 function changebonds(state::InfiniteMPS, H, alg::VUMPSSvdCut, envs=environments(state, H))
     if (length(state) == 1)
         return changebonds_1(state, H, alg, envs)
     else
-        return changebonds_n(state, H, alg, envs)
+        @static if Defaults.parallelize_sites
+            return changebonds_parallel_n(state, H, alg, envs)
+        else
+            return changebonds_n(state, H, alg, envs)
+        end
     end
 end