code: def constant_coefficients(d, timelines, constant=True, independent=0):
      
      return time_varying_coefficients(d, timelines, constant, independent=independent, randgen=random.normal)
docs: Proportional hazards model.
  
      d: the dimension of the dataset
      timelines: the observational times
      constant: True for constant coefficients
      independent: the number of coffients to set to 0 (covariate is ind of survival), or
        a list of covariates to make indepent.
  
      returns a matrix (t,d+1) of coefficients