def METHOD_NAME(self, rate, ydot_j, y_i):
    """
    return a sympy expression containing the term in a jacobian matrix
    in a reaction network corresponding to this rate
    Returns the derivative of the j-th YDOT wrt. the i-th Y
    If the derivative is zero, returns 0.
    ydot_j and y_i are objects of the class 'Nucleus'
    """
    ydot_sym = self.ydot_term_symbol(rate, ydot_j)
    deriv_sym = sympy.symbols(f'Y__j{y_i}__')
    jac_sym = sympy.diff(ydot_sym, deriv_sym)
    symbol_is_null = False
    if jac_sym.equals(0):
        symbol_is_null = True
    return (jac_sym.evalf(n=self.float_explicit_num_digits), symbol_is_null)