Proposed changes

Upgrade instructions

If using ErrorControl to choose a step size for local time stepping, you may have to tighten the error tolerances specified in the input file. The code previously often kept the actual error estimate significantly lower than the specified tolerance.

Code review checklist

• The code is documented and the documentation renders correctly. Run
  make doc to generate the documentation locally into BUILD_DIR/docs/html.
  Then open index.html.
• The code follows the stylistic and code quality guidelines listed in the
  code review guide.
• The PR lists upgrade instructions and is labeled bugfix or
  new feature if appropriate.

Further comments