A highly flexible tool for large scale computational problems in applied physics. A software package is described, the Simulation Generator (SimGen), which automatically constructs a computer simulation from a high level description of a physical problem. SimGen constructs a simulation by (i) parsing the input file, (ii) generating by symbolic manipulation the functions which are needed for a Newton method solution of the problem, and (iii) interfacing the computer generated code to an appropriate solution module. Executing the simulation solves the equations specified in the input file. The choice of numerical representation of the problem (e.g. type of finite difference scheme for a coupled set of nonlinear partial differential equations) is left to the user. Emphasis in the design of this software has been placed on generality and flexibility. The calculation of the elements of the Jacobian matrix, which is needed by Newton’s method, is discussed. The syntax of the input file is well suited to specifying large sets of discrete equations. To show the ease and flexibility of the approach a semiconductor simulation is presented.