Fix FixedSpaceTruncation for simple update (#202)

Author: Yue-Zhengyuan

src/algorithms/time_evolution/evoltools.jl

@@ -141,11 +141,13 @@ function _apply_gate(
     trscheme::TruncationScheme,
 ) where {T<:Number,S<:ElementarySpace}
     @tensor a2b2[-1 -2; -3 -4] := gate[-2 -3; 1 2] * a[-1 1 3] * b[3 2 -4]
-    return tsvd!(
-        a2b2;
-        trunc=((trscheme isa FixedSpaceTruncation) ? truncspace(space(a, 3)) : trscheme),
-        alg=TensorKit.SVD(),
-    )
+    trunc = if trscheme isa FixedSpaceTruncation
+        V = space(b, 1)
+        truncspace(isdual(V) ? V' : V)
+    else
+        trscheme
+    end
+    return tsvd!(a2b2; trunc, alg=TensorKit.SVD())
 end
 
 """

src/algorithms/time_evolution/simpleupdate3site.jl

@@ -239,7 +239,8 @@ function _get_allprojs(Ms, Rs, Ls, trunc::TensorKit.TruncationScheme, revs::Vect
     N = length(Ms)
     projs_errs = map(1:(N - 1)) do i
         trunc2 = if isa(trunc, FixedSpaceTruncation)
-            truncspace(space(Ms[i + 1], 1))
+            V = space(Ms[i + 1], 1)
+            truncspace(isdual(V) ? V' : V)
         else
             trunc
         end