Remove trailing coefficients
Remove trailing coefficients until a coefficient is reached whose absolute value greater than tol or the beginning of the series is reached. If all the coefficients would be removed the series is set to . A new series instance is returned with the new coefficients. The current instance remains unchanged.
tol : non-negative number.
All trailing coefficients less than tol will be removed.
new_series : series
Contains the new set of coefficients.