## *GREEN

Keyword type: step

This procedure is used to calculate the Green function due to unit forces at specific nodes in specific global directions. The Green functions are calculated for each unit force separately. The unit forces are defined by a *CLOAD card (the force value specified by the user is immaterial, a unit force is taken). For details the user is referred to Section 6.9.24.

There are two optional parameters: SOLVER and STORAGE. SOLVER specifies which solver is used to perform a decomposition of the linear equation system. This decomposition is done only once. It is repeatedly used in determining all Green functions. The following solvers can be selected:

• the SGI solver
• PaStiX
• PARDISO
• SPOOLES [3,4].
• TAUCS

Default is the first solver which has been installed of the following list: SGI, PaStiX, PARDISO, SPOOLES and TAUCS. If none is installed, a Green function calculation is not possible.

The SGI solver should by now be considered as outdated.SPOOLES is very fast, but has no out-of-core capability: the size of systems you can solve is limited by your RAM memory. With 32GB of RAM you can solve up to 1,000,000 equations. TAUCS is also good, but my experience is limited to the decomposition, which only applies to positive definite systems. It has an out-of-core capability and also offers a decomposition, however, I was not able to run either of them so far. PARDISO is the Intel proprietary solver and is about a factor of two faster than SPOOLES. The most recent solver we tried is the freeware solver PaStiX from INRIA. It is really fast and can use the GPU. For large problems and a high end Nvidea graphical card (32 GB of RAM) we got an acceleration of a factor between 3 and 8 compared to PARDISO. We modified PaStiX for this, therefore you have to download PaStiX from our website and compile it for your system. This can be slightly tricky, however, it is worth it!

The parameter STORAGE indicates whether the scalar frequencies, Green functions, mass and stiffness matrix should be stored in binary form in file jobname.eig for further use in a *SENSITIVITY procedure. Default is STORAGE=NO. Specify STORAGE=YES if storage is requested.

First line:

• *GREEN
• Enter SOLVER, if needed, and its value.

Example:

*GREEN,SOLVER=PARDISO


defines a Green function step and selects the PARDISO solver as linear equation solver. For this to work, the PARDISO solver must have been linked with CalculiX.

Example files: green1.