code: def mean_forecast_err(y, yhat):
      return y.sub(yhat).mean()
  
imports: import numpy
  from scipy import stats
  import pandas
  import matplotlib.pyplot
  import statsmodels.api
  from statsmodels.graphics.api import qqplot
label_desc: Use image node_id 1 for calling a global function with example usage: mean_forecast_err(y, yhat) and returns: y