  High-quality ordinary differential equation (ODE) solver libraries have a
long history, going back to the 1970s. Over the past several years we have
implemented, on top of the PETSc linear and nonlinear solver package, a new
general-purpose, extensive, extensible library for solving ODEs and
differential algebraic equations (DAEs). Package includes support for both
forward and adjoint sensitivities that can be easily utilized by the TAO
optimization package, which is also part of PETSc. The ODE/DAE integrator
library strives to be highly scalable but also to deliver high efficiency for
modest-sized problems. The library includes explicit solvers, implicit solvers,
and a collection of implicit-explicit solvers, all with a common user interface
and runtime selection of solver types, adaptive error control, and monitoring
of solution progress. The library also offers enormous flexibility in selection
of nonlinear and linear solvers, including the entire suite of PETSc iterative
solvers, as well as several parallel direct solvers.
