code: def forward(ctx, q, k):
      w = torch.einsum(
          "ncq,nck->nqk", q, k / math.sqrt(k.shape[1])
      ).softmax(dim=2)
      ctx.save_for_backward(q, k, w)
      return w
  
imports: import math
  import numpy
  import torch
  import torch.nn
  from torch.cuda.amp import custom_bwd, custom_fwd
label_desc: Use image node_id 1 for calling the StableAttentionOp obj's underlying member method code with example usage: obj.forward(ctx, q, k) and returns: w