Thanks for your response @CatalinaAlbornoz

Part of the code that is giving error is as follows:

```
t = np.arange(0, 20, 0.1) # Time from 0 to 200 with step size of 0.1
x_in = torch.tensor(np.cos(t))
print(x_in.shape)
"""
target=x_in+torch.torch.tensor(0.03)
"""
nb=3
na=3
D=3
list1=torch.randn(3,6, requires_grad=True)
print(f" list1 before training:{list1}")
list2=torch.randn(3,6, requires_grad=True)
list3=torch.randn(3,6, requires_grad=True)
evolution_time=torch.randn(1,requires_grad=True)
list_single = [0.52, 0.7, 0.41,0.23, 0.24, 0.4]
list_double=[0.31,0.51,0.42,0.3,0.4,0.5,0.66,0.33,0.22,0.7]#10 elements
#NOTE:list_single,double are not parameters as per the paper
def apply_hamiltonian(H, time):
# This function applies the Hamiltonian gate (time evolution)
qml.templates.ApproxTimeEvolution(H, time, 1)
dev = qml.device("default.qubit", wires=6)
s=[]
@qml.qnode(dev,diff_method="backprop")
def circuit(nb,x_in,D,na,list1,list2,list3,list_single,list_double,evo_time):
for i in range(len(x_in)):
s2=[]
for j in range(nb):
s2.append(0)
s.append(s2)
s1=torch.zeros(len(x_in),nb)
for i in range(len(x_in)):#loop for every time step
# Apply gates for encoding
for j in range(nb):
qml.RY(np.arccos(x_in[i]),wires=j)
for turn in range(D): # no. of layers
for r in range(na+nb): # single qubi part of U(theta in paper)
qml.RX(list1[turn,r],wires=r)
qml.RZ(list2[turn,r],wires=r)
qml.RX(list3[turn,r],wires=r)
coeff_list=list_single+list_double
obs1=[qml.PauliX(i) for i in range(na+nb)]
obs2=[qml.PauliZ(k3) @ qml.PauliZ(k4) for k3 in range(1,na+nb)
for k4 in range(k3-1)]
obs=obs1+obs2
# Construct the Hamiltonian
H = qml.Hamiltonian(coeff_list, obs)
#applying time approximate Hamiltonian gate
apply_hamiltonian(H, evo_time)
#qml.templates.ApproxTimeEvolution(H, time, 1)
m=torch.zeros(len(x_in))
for k1 in range(nb):
s[i][k1]=qml.measure([k1],reset=True)
#print(f"time step:{i} complete")
# m[i]=qml.expval(s[i][0])
k=[]
for i in range(len(x_in)):
for j in range(nb):
k.append(qml.expval(s[i][j]))
return k
#return(qml.expval(s[0][0]),qml.expval(s[0][1]),qml.expval(s[0][2]),qml.expval(s[1][0]),qml.expval(s[1][1]),qml.expval(s[1][2]))
#return(qml.expval(qml.PauliX(0)@qml.PauliX(1)@qml.PauliX(2)))
#w=circuit(3, x_in, 3, 3)
#print(circuit(3, x_in, 3, 3,list1,list2,list3,list_single,list_double,evolution_time))
rnn=circuit(3, x_in, 3, 3,list1,list2,list3,list_single,list_double,evolution_time)
time_steps=len(x_in)
```

How to get rid of the error that I said earlier?

It will be helpful if you please do explain in more details about the way out you pointed out to solve this problem in your earlier post.