# How to propagate neural network gradients through a Networkx graph?

I'm trying to train my neural network to make every edge's weight in the graph to be `10`. I'm starting out by generating random points (`inp`), and make each 2 adjacent points (using `idx`) have an edge with `weight = 1`. And then if the 2 adjacent points already have an edge, the edge's weight is being sent to the NN that outputs what additional weight to add to it.

``````import warnings
warnings.filterwarnings("ignore", category=UserWarning)

import torch
import torch.nn as nn
import networkx as nx
import matplotlib.pyplot as plt
import torch.optim as optim

class Net(nn.Module):
def __init__(self):
super(Net, self).__init__()
self.fc1 = nn.Linear(1,3)
self.fc2 = nn.Linear(3,1)

def forward(self, x):
x = self.fc1(x)
x = self.fc2(x)
return x

g = nx.DiGraph()
model = Net()
optimizer = optim.Adam(model.parameters(), lr = 1e-3)

def training(n_iter):
for epoch in range(n_iter):
print(epoch)
inp = torch.randint(0,10,(20,))
idx = 0
while idx < len (inp) - 1:
if  g.has_edge(inp[idx].item(), inp[idx+1].item()): #edge exist

edge_weight = g[inp[idx].item()][inp[idx+1].item()]["weight"]
edge_weight_tensor = torch.tensor([edge_weight]).float() #to tensor

added_edge_weight = model(edge_weight_tensor) #value from network
idx +=1
else:
idx +=1

edges = g.edges()
weights = [g[u][v]['weight'] for u,v in edges]

loss_list = [w for w in weights if not isinstance(w, int)] #only take tensors
try:
loss_tensors = (torch.stack(loss_list, dim=0)-10)
loss_square = torch.square(loss_tensors)
loss = torch.sum(loss_square)
print(loss)
except RuntimeError: #no tensors - hence create a 0 loss
loss = torch.tensor(0.0, requires_grad = True)

loss.backward(retain_graph=True)
optimizer.step()
return weights

weights = training(5)

#plot
plt.figure(figsize=(6,6))
pos = nx.spring_layout(g, k = 0.5)

nx.draw(g, with_labels=True, node_color='skyblue', font_weight='bold',  width=weights, pos=pos)
``````

My issue is that I'm not sure that the gradients can propagate this way, and also that it doesn't seem like I can add the NN weight addition to the edge's weight-- getting the following error:

``````RuntimeError: one of the variables needed for gradient computation has been modified by an inplace operation: [torch.FloatTensor [3, 1]], which is output 0 of TBackward, is at version 2; expected version 1 instead. Hint: enable anomaly detection to find the operation that failed to compute its gradient, with torch.autograd.set_detect_anomaly(True).
``````