The Simulation Problem Analysis Research Kernel (SPARK) environment for simulation of nonlinear differential algebraic systems has been revised to improve modeling convenience, modeling flexibility, and solution efficiency. Solution efficiency has been enhanced by automatic decomposition of the problem into strongly connected components, characterized as separately solvable subproblems. The normally constructed data flow graph in SPARK allows such components to be identified and placed in the correct order for sequential solution resulting in significant speed?up for problems that are not strongly interconnected. Modeling flexibility has been enhanced by adding Multivalued Objects. Whereas conventional SPARK objects represent single equations, and produce a single result, this extension allows more complex objects which themselves solve simultaneous sets of equations for multiple results. The need for such objects arises when submodels are to be solved independently of the SPARK solver; e.g., to use a specially tailored algorithm. With regard to modeling convenience, the graphical user interface now allows model definition by selection and placement of object icons in a graphical window in an X-windows environment. These objects can be connected with macro links comprising multiple problem variables. The resulting problem is then translated into a Network Language Specification file for SPARK processing.