def update(self, z, R=None, H=None):
        """
        Add a new measurement (z) to the Kalman filter. If z is None, nothing
        is changed.

        Parameters
        ----------

        z : np.array
            measurement for this update.

        R : np.array, scalar, or None
            Optionally provide R to override the measurement noise for this
            one call, otherwise  self.R will be used.

        H : np.array,  or None
            Optionally provide H to override the measurement function for this
            one call, otherwise  self.H will be used.
        """

        if H is None:
            H = self.H

        # new probability is recursively defined as prior * likelihood
        for i, f in enumerate(self.filters):
            f.update(z, R, H)
            self.p[i] *= f.likelihood

        self.p /= sum(self.p) # normalize

        # compute estimated state and covariance of the bank of filters.
        self.P = np.zeros(self.filters[0].P.shape)

        # state can be in form [x,y,z,...] or [[x, y, z,...]].T
        is_row_vector = (self.filters[0].x.ndim == 1)
        if is_row_vector:
            self.x = np.zeros(self.dim_x)
            for f, p in zip(self.filters, self.p):
                self.x += np.dot(f.x, p)
        else:
            self.x = np.zeros((self.dim_x, 1))
            for f, p in zip(self.filters, self.p):
                self.x = np.zeros((self.dim_x, 1))
                self.x += np.dot(f.x, p)

        for x, f, p in zip(self.x, self.filters, self.p):
            y = f.x - x
            self.P += p*(np.outer(y, y) + f.P)


        # save measurement and posterior state
        self.z = deepcopy(z)
        self.x_post = self.x.copy()
        self.P_post = self.P.copy()
Add a new measurement (z) to the Kalman filter. If z is None, nothing
        is changed.

        Parameters
        ----------

        z : np.array
            measurement for this update.

        R : np.array, scalar, or None
            Optionally provide R to override the measurement noise for this
            one call, otherwise  self.R will be used.

        H : np.array,  or None
            Optionally provide H to override the measurement function for this
            one call, otherwise  self.H will be used.