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		Trellis is a software framework developed in C++ to make up a reusable design for software to solve problems in geometrically based numerical mechanics. As a framework Trellis dictates the architecture of the specific application written by the user of Trellis implementing a specific analysis. Most of the arising design decisions are made, and the analysis programmer can concentrate on the problem specific implementation, i.e. he has to provide the actual problem specific functions that Trellis will call to solve the problem. Problem specific functions are all those functions that are specific to the analysis that is being solved. Usually that will be at least the contribution of each integration point to the global system matrix or the the right hand side of the system. Trellis contains classes that represent the frame of a numerical analysis, e.g. knowing how to integrate over certain geometric entities (like e.g. tetrahedral elements) or how to solve non-linear problems using e.g. a Newton algorithm. Those classes were designed by identifying independent objects of numerical methods in general rather than just defining FE-elements or nodes as objects as it is done in many object oriented FE-codes. As a result Trellis' problem specific part is e.g. completely independent of the polynomial order of the shape functions used. Even the numerical method can be changed, and the same problem can be solved using partition of unity methods instead of Finite Element methods without the need to change the problem specific part provided by the analysis programmer. After the algorithms for an analysis are coded three input files have to be provided, the geometric model, the discretization, and an attribute file. The geometric model has to be created using a commercial geometric modeler. Currently there are interfaces for the following geometric modeler available that can be used to create the geometric model Shapes Acis Parasolid In the case of solving the problem using finite elements the discretizations being created from the geometric model using the SCOREC meshing environment MEGA. or other automatic mesh generator. The meshing is done fully automatically based on specifications that control the size of the elements for the entities of the geometric model. The attribute file contains all the information needed for an analysis (boundary conditions, initial conditions etc.), and attributes that control the solution process (linear/non-linear solver, polynomial order of the shape functions etc.). The attribute system supports the use of expressions dependent on spacial coordinates or time attributed to entities of the geometric model.
				Andrew Bauer