code: def compute_grad(gh: DataFrame, label, score):
      gh["g"] = 2 * (score["score"] - label)
  
imports: import numpy
  import pandas
  import torch
  from fate.arch.dataframe import DataFrame
  from scipy.special import expit
  from fate.ml.utils.predict_tools import BINARY, MULTI, REGRESSION
label_desc: Use image node_id 4 for calling the L2Loss obj's underlying member method code with example usage: obj.compute_grad(gh, label, score) without return types