PETSc, the Portable, Extensible Toolkit for Scientific Computation, includes a large suite of scalable parallel linear and nonlinear equation solvers, ODE integrators, and optimization algorithms for application codes written in C, C++, Fortran, and Python. In addition, PETSc includes support for managing parallel PDE discretizations including parallel matrix and vector assembly routines. Toolkits/libraries that use PETSc.