code: def _var_bounds(self):
          
          x0 = array([])
          xmin = array([])
          xmax = array([])
  
          for var in self.om.vars:
              x0 = r_[x0, var.v0]
              xmin = r_[xmin, var.vl]
              xmax = r_[xmax, var.vu]
  
          return x0, xmin, xmax
docs: Returns bounds on the optimisation variables.