Autodesk Nastran Solver Options

The solver options found in the Simulation Mechanical Analysis Parameters dialog boxes are not mapped to equivalent Nastran parameters. The default solver parameter (automatic) is specified for each of the following three situations:

When you run a solution within Simulation Mechanical using the Nastran processor
When you export a model to the Autodesk Nastran Editor
When you create a Nastran deck using the Export Third-Party FEA command.¹

How to Specify a User-Defined Solver Option

There are three methods you can use to specify a user-defined solver option for Nastran analyses:

Run the solver (Nastran.exe) from the command line. Include the parameter DECOMPMETHOD and set it equal to a valid Autodesk / NEi-specific Nastran solver option.
The file Nastran.exe is installed in the Nastran Engine subfolder of your Simulation Mechanical installation folder. The default path is C:\Program Files\Autodesk\Simulation 20xx\Nastran Engine. Detailed instructions for running Nastran solutions from a command line are beyond the scope of this Help publication.
Edit the file, Nastran.INI, located in the Nastran Engine subfolder of your Simulation Mechanical installation folder. Edit the value of the DECOMPMETHOD entry, which is within the [Program Control Directives] section of the file.
Edit the exported Nastran deck using Windows® Notepad or similar text editor. Add an NEi / Autodesk-specific NASTRAN executive card (NASTRAN DECOMPMETHOD=valid solver option ).

NEi / Autodesk Nastran-Specific Solver Options

Directive	Description	Options	Default Option
DECOMPMETHOD	Decomposition method: PCGLSS – Selects the parallel sparse iterative solver, available in all linear and nonlinear static solutions. This solver is recommended for large problems and will generally be faster than the VSS solver. VSS – Selects the sparse direct solver, available in all solutions. This solver is recommended for most problems. Significant performance degradation can occur if the RAM directive is set too low and an out of core solution is performed and/or physical memory is limited. The PCGLSS solver should be faster for these types of problems. VIS – Selects the sparse iterative solver, available in all except eigenvalue solutions. If the VIS solver is selected for an eigenvalue solution, the VSS solver will be used. This solver is recommended for static solutions of models consisting mostly of solid elements. It can be significantly faster that the VSS solver in some cases and uses less resources (memory and disk space). PSS – Selects the parallel sparse direct solver, available in all solutions. This solver will be generally faster than the VSS solver, especially on multiple CPU machines, but may require more memory. AUTO – The program picks the best method based on the RAM directive setting, material properties, model size, and solution selected in the model.	PCGLSS VSS VIS PSS AUTO	AUTO

Directive

Description

Options

Default Option

DECOMPMETHOD

Decomposition method:

PCGLSS – Selects the parallel sparse iterative solver, available in all linear and nonlinear static solutions. This solver is recommended for large problems and will generally be faster than the VSS solver.
VSS – Selects the sparse direct solver, available in all solutions. This solver is recommended for most problems. Significant performance degradation can occur if the RAM directive is set too low and an out of core solution is performed and/or physical memory is limited. The PCGLSS solver should be faster for these types of problems.
VIS – Selects the sparse iterative solver, available in all except eigenvalue solutions. If the VIS solver is selected for an eigenvalue solution, the VSS solver will be used. This solver is recommended for static solutions of models consisting mostly of solid elements. It can be significantly faster that the VSS solver in some cases and uses less resources (memory and disk space).
PSS – Selects the parallel sparse direct solver, available in all solutions. This solver will be generally faster than the VSS solver, especially on multiple CPU machines, but may require more memory.
AUTO – The program picks the best method based on the RAM directive setting, material properties, model size, and solution selected in the model.

PCGLSS

VSS

VIS

PSS

AUTO

¹Note: If you are editing a Nastran deck created using the Export Third-Party FEA command, use directives and options that are consistent with MSC Nastran conventions. Consult the MSC Nastran program documentation for more information.