diff --git a/spin_systems/__pycache__/Hamiltonians.cpython-38.pyc b/spin_systems/__pycache__/Hamiltonians.cpython-38.pyc
index 361f13e..4e8bd96 100644
Binary files a/spin_systems/__pycache__/Hamiltonians.cpython-38.pyc and b/spin_systems/__pycache__/Hamiltonians.cpython-38.pyc differ
diff --git a/spin_systems/__pycache__/__init__.cpython-38.pyc b/spin_systems/__pycache__/__init__.cpython-38.pyc
index ca7c142..7a960ce 100644
Binary files a/spin_systems/__pycache__/__init__.cpython-38.pyc and b/spin_systems/__pycache__/__init__.cpython-38.pyc differ
diff --git a/spin_systems/__pycache__/iHamiltonians.cpython-38.pyc b/spin_systems/__pycache__/iHamiltonians.cpython-38.pyc
new file mode 100644
index 0000000..f53f692
Binary files /dev/null and b/spin_systems/__pycache__/iHamiltonians.cpython-38.pyc differ
diff --git a/spin_systems/iHamiltonians.py b/spin_systems/iHamiltonians.py
index 180bfad..5540c79 100644
--- a/spin_systems/iHamiltonians.py
+++ b/spin_systems/iHamiltonians.py
@@ -10,7 +10,7 @@ def IsingChainWithAncilla(J=1., h_z=0.25, h_x=0.):
     sx_sys = np.kron(sx,Id2)
     
     sz_anc = np.kron(Id2,sz)
-    sx_anc = np.kron(Id2,sz)
+    sx_anc = np.kron(Id2,sx)
 
     H  = -J*(np.kron(sx_sys,sx_sys))-h_z*(np.kron(sz_sys,Id4)+np.kron(Id4,sz_sys))-h_x*(np.kron(sx_sys,Id4)+np.kron(Id4,sx_sys))
     H  -= -J*(np.kron(sx_anc,sx_anc))-h_z*(np.kron(sz_anc,Id4)+np.kron(Id4,sz_anc))-h_x*(np.kron(sx_anc,Id4)+np.kron(Id4,sx_anc))
diff --git a/tensors/__pycache__/iMatrixProductState.cpython-38.pyc b/tensors/__pycache__/iMatrixProductState.cpython-38.pyc
index 3d70e3d..79c227c 100644
Binary files a/tensors/__pycache__/iMatrixProductState.cpython-38.pyc and b/tensors/__pycache__/iMatrixProductState.cpython-38.pyc differ
diff --git a/tensors/iMatrixProductState.py b/tensors/iMatrixProductState.py
index 2799fd2..d6beb6a 100644
--- a/tensors/iMatrixProductState.py
+++ b/tensors/iMatrixProductState.py
@@ -50,10 +50,12 @@ def compute_transfer_matrix(self):
         T   = oe.contract('abe,ehf,cbd,dhg->acfg',self.B1,self.B2,self.B1.conj(),self.B2.conj())
         self.Tnot_reshaped = T.copy()
         self.T = T.reshape(shp1[0]**2,shp1[0]**2)    
+        
     def compute_corr_length(self):
         self.compute_transfer_matrix()
-        eigs = np.sort(np.abs(np.linalg.eigvals(self.T)))[::-1]
-        return -2./np.log(eigs[1])
+        eig =np.sort(  np.abs(eigs(self.T, k=6, ncv=300, which='LM',return_eigenvectors=False)) )[::-1]
+        self.Teig = eig
+        return -2./np.log(eig[1])
         
     def compute_long_distance_observable_degenerate(self,op):
         self.compute_transfer_matrix()