class_docstr: Exchangeable working covariance for QIF regression.
code: def mat(self, dim, term):
      if term == 0:
          return np.eye(dim)
      elif term == 1:
          return np.ones((dim, dim))
      else:
          return None
  
imports: import numpy
  from collections import defaultdict
  import statsmodels.base.model
  from statsmodels.genmod import families
  from statsmodels.genmod.generalized_linear_model import GLM
  from statsmodels.genmod.families import links
  from statsmodels.genmod.families import varfuncs
  import statsmodels.regression.linear_model
  import statsmodels.base.wrapper
  from statsmodels.tools.decorators import cache_readonly
label_desc: Use image node_id 2 for calling the QIFExchangeable obj's underlying member method code with example usage: obj.mat(dim, term) and returns: np, np, None