Set the code to use trapezoidal integration.

        **Call signature**

        *n*
          Use this many nodes
        Returns
          *self* for convenience in chaining.

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