I defined four tensors that represent index_x,index_y,index_z,and value,respectively and assigned value to a new tensor using these three index. Why were the results of the two assignments different?

```
import torch
import numpy as np
import random
import os
def seed_torch(seed=0):
random.seed(seed)
np.random.seed(seed)
os.environ['PYTHONHASHSEED'] = str(seed)
torch.manual_seed(seed)
torch.cuda.manual_seed(seed)
torch.cuda.manual_seed_all(seed)
torch.backends.cudnn.deterministic = True
torch.backends.cudnn.benchmark = False
seed_torch(1)
a_list, b_list, c_list = [], [], []
for i in range(0, 512*512):
a_ = random.randint(0, 399)
b_ = random.randint(0, 399)
c_ = random.randint(0, 199)
a_list.append(a_)
b_list.append(b_)
c_list.append(c_)
a = torch.tensor(a_list)
b = torch.tensor(b_list)
c = torch.tensor(c_list)
v = torch.rand(512*512)
matrix1 = torch.zeros(400,400,200)
matrix2 = torch.zeros(400,400,200)
index=[a,b,c]
matrix1[index]=v
matrix2[index]=v
m = matrix1 - matrix2
print(m.sum())
```

print(m.sum()) is not zero