def Rder(x, alpha , beta, gamma):
    """Calculates the derivative with respect x1 of the first dimension of the function R() 

        Parameters
        -------
        x : array of shape (N,)
            first dimension of state at a single timepoint
        alpha, beta, gamma : floats
            parameter of sigle FutzHugh-Nagumo nodes

        Returns
        -------
        R : array of shape (N,)
           d/dx1 ( -alpha* x1**3 + beta *x1**2 - gamma* x1 )

    """
    return -3*alpha* x**2 + 2*beta*x - gamma