docs: def set_trapezoidal_integration(self, n):
          """Set the code to use trapezoidal integration.
  
          **Call signature**
  
          *n*
            Use this many nodes
          Returns
            *self* for convenience in chaining.
  
          """
          if not (n >= 2):
              raise ValueError('must have n >= 2; got %r' % (n,))
  
          self.in_vals[IN_VAL_INTEG_METH] = n + 1
          return self