ensure positive QR/LQ in IDMRG

Author: lkdvos

src/algorithms/groundstate/idmrg.jl

@@ -159,9 +159,9 @@ function _localupdate_sweep_idmrg!(ψ, H, envs, alg_eigsolve)
         _, ψ.AC[pos] = fixedpoint(h, ψ.AC[pos], :SR, alg_eigsolve)
         if pos == length(ψ)
             # AC needed in next sweep
-            ψ.AL[pos], ψ.C[pos] = left_orth(ψ.AC[pos])
+            ψ.AL[pos], ψ.C[pos] = left_orth(ψ.AC[pos]; positive = true)
         else
-            ψ.AL[pos], ψ.C[pos] = left_orth!(ψ.AC[pos])
+            ψ.AL[pos], ψ.C[pos] = left_orth!(ψ.AC[pos]; positive = true)
         end
         transfer_leftenv!(envs, ψ, H, ψ, pos + 1)
     end
@@ -171,7 +171,7 @@ function _localupdate_sweep_idmrg!(ψ, H, envs, alg_eigsolve)
         h = AC_hamiltonian(pos, ψ, H, ψ, envs)
         E, ψ.AC[pos] = fixedpoint(h, ψ.AC[pos], :SR, alg_eigsolve)
 
-        ψ.C[pos - 1], temp = right_orth!(_transpose_tail(ψ.AC[pos]; copy = (pos == 1)))
+        ψ.C[pos - 1], temp = right_orth!(_transpose_tail(ψ.AC[pos]; copy = (pos == 1)); positive = true)
         ψ.AR[pos] = _transpose_front(temp)
 
         transfer_rightenv!(envs, ψ, H, ψ, pos - 1)