0fc25715a1
* fix * fix copies * remove heun from tests * add back heun and fix the tests to include 2nd order * fix the other test too * Apply suggestions from code review * Apply suggestions from code review * Apply suggestions from code review * make style * add more comments --------- Co-authored-by: yiyixuxu <yixu310@gmail,com> Co-authored-by: Patrick von Platen <patrick.v.platen@gmail.com>