Confusing code

[hxtruong6]

Hi, I am trying to re-implement SDNE code but I got stuck when reading code. Could you explain for me these below lines:
-

GraphEmbedding/ge/models/sdne.py

Line 162 in 7de7a09

edge_weight = graph[v1][v2].get('weight', 1)

: what is meaning of get('weight',1). Why does it has 1 value here?

• GraphEmbedding/ge/models/sdne.py

  Line 169 in 7de7a09

  A_ = sp.csr_matrix((A_data + A_data, (A_row_index + A_col_index, A_col_index + A_row_index)),

  : what is A_ and its purpose?

• GraphEmbedding/ge/models/sdne.py

  Line 172 in 7de7a09

  D = sp.diags(A_.sum(axis=1).flatten().tolist()[0])

  : how does this line create a diagonal matrix? I suppose this is a formula.

• GraphEmbedding/ge/models/sdne.py

  Line 125 in 7de7a09

  L_mat_train = self.L[index][:, index].todense()

  : this is code to get L[i:j, :] for a mini batch to train. But what is meaning of L[index][:, index].todense() with index = [i:j]

• GraphEmbedding/ge/models/sdne.py

  Line 46 in 7de7a09

  def loss_1st(y_true, y_pred):

  : where place do you pass parameterss for Loss function? How to know L = y_true and Y = y_pred?

Thank your helping!