code: def backward(cls, ctx, dY):
      (Y,) = ctx.saved_tensors
      gppr = Y.sqrt()  # = 1 / g'' (Y)
      dX = dY * gppr
      q = dX.sum(ctx.dim) / gppr.sum(ctx.dim)
      q = q.unsqueeze(ctx.dim)
      dX -= q * gppr
      return dX, None, None
  
imports: import torch
  import torch.nn
  from torch.autograd import Function
label_desc: Use image node_id 2 for calling the Entmax15Function obj's underlying member method code with example usage: obj.backward(cls, ctx, dY) and returns: dX,  None,  None