ct 7 Two different modifications of Popovski's method are developed, both are free of second derivatives. In the first mod8 ified scheme we traded the second derivative by an additional function evaluation. In the second method we replaced the 9 second derivative by a finite difference and thus reducing the order slightly and reducing the number of evaluations per step 10 by one. Therefore the second modification is more efficient. 11 Published by Elsevier Inc.
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