====== TR-BDF2 ======

Implicit multistep solver implementation of TR-BDF2, which is an implicit Runge-Kutta formula with a first stage that is a trapezoidal rule step and a second stage that is a backward differentiation formula of second order.

Applicable for **stiff** problems of **low** accuracy.

Applicable [[Solver_settings|solver settings]]:

  * Absolute tolerance
  * Relative tolerance
  * Initial step size
  * Max step size
  * Min step size
  * Refine
  * Limit data points to last
  * Norm Control
  * Allowed step size violations
  * Enable saturation
  * LU decomposition matrix format

===== Reference =====

  * Shampine, L. F. and M. E. Hosea, “Analysis and Implementation of TR-BDF2,” //Applied Numerical Mathematics// 20, 1996.
  * Bank, R. E., W. C. Coughran, Jr., W. Fichtner, E. Grosse, D. Rose, and R.Smith, “Transient Simulation of Silicon Devices and Circuits”, //IEEE Trans. CAD//, 4 (1985), pp 436-451.