Hello all, I am encountering In place operation error when I am trying to index a leaf variable to update gradients with customized Shrink function. I cannot work around it. Any help is highly appreciated!

```
import torch.nn as nn
import torch
import numpy as np
from torch.autograd import Variable, Function
# hyper parameters
batch_size = 100 # batch size of images
ld = 0.2 # sparse penalty
lr = 0.1 # learning rate
x = Variable(torch.from_numpy(np.random.normal(0,1,(batch_size,10,10))), requires_grad=False) # original
# depends on size of the dictionary, number of atoms.
D = Variable(torch.from_numpy(np.random.normal(0,1,(500,10,10))), requires_grad=True)
# hx sparse representation
ht = Variable(torch.from_numpy(np.random.normal(0,1,(batch_size,500,1,1))), requires_grad=True)
ht_ori = ht
# Dictionary loss function
loss = nn.MSELoss()
# customized shrink function to update gradient
shrink_ht = lambda x: torch.stack([torch.sign(i)*torch.max(torch.abs(i)-lr*ld,0)[0] for i in x])
### sparse reprsentation optimizer_ht single image.
# optimizer_ht = torch.optim.SGD([ht,D], lr=lr, momentum=0.9)
optimizer_ht = torch.optim.SGD([ht], lr=lr, momentum=0.9) # optimizer for sparse representation
#optimizer_ht.zero_grad() # clear up gradients
## update from resconstruction
#loss_ht = 0.5*torch.norm((x-(D*ht).sum(dim=0)),p=2)**2
#loss_ht.backward() # back propogation and calculate gradients
#optimizer_ht.step() # update parameters with gradients
## update for the batch
for idx in range(len(x)):
optimizer_ht.zero_grad() # clear up gradients
loss_ht = 0.5*torch.norm((x[idx]-(D*ht[idx]).sum(dim=0)),p=2)**2
loss_ht.backward() # back propogation and calculate gradients
optimizer_ht.step() # update parameters with gradients
ht[idx] = shrink_ht(ht[idx]) # customized shrink function.
```

RuntimeError Traceback (most recent call last)

in ()

15 loss_ht.backward() # back propogation and calculate gradients

16 optimizer_ht.step() # update parameters with gradients

â€”> 17 ht[idx] = shrink_ht(ht[idx]) # customized shrink function.

18

19

/home/miniconda3/lib/python3.6/site-packages/torch/autograd/variable.py in **setitem**(self, key, value)

85 return MaskedFill.apply(self, key, value, True)

86 else:

â€”> 87 return SetItem.apply(self, key, value)

88

89 def **deepcopy**(self, memo):

RuntimeError: a leaf Variable that requires grad has been used in an in-place operation.

**Specifically, this line of code below seems** give error as it index and update leaf variable at the same time. how

```
ht[idx] = shrink_ht(ht[idx]) # customized shrink function.
```

Could you help? Thanks!

W.S.