SUNDIALS中的RTOL和ATOL

1. Relative tolerance (RTOL) controls local error relative to the size of the solution— RTOL = 10-4 means that errors are controlled to 0.01%
2. Absolute tolerances (ATOL) control error when a solution component may be small
   — Ex: solution starting at a nonzero value but decaying to noise level, ATOL should be set to noise level