The solution time grows linearly with problems size for iterative methods so huge models can still be
solved within very reasonable times. For modal analyses of large models (e.g., 10 million DOF or larger),
MODOPT,LANPCG is a viable solution method if the number of modes is limited to approximately 100.
Use MSAVE,ON (the default in most cases) for memory savings of up to 70 percent. The MSAVE command
uses an element-by-element approach (rather than globally assembling the stiffness matrix) for the
parts of the structure involving SOLID185,SOLID186, or SOLID187 elements with linear material properties.
This feature applies only to static analyses or modal analyses using the PCG Lanczos method (AN-
TYPE,STATIC; or ANTYPE,MODAL with MODOPT,LANPCG). Note that the MSAVE feature does not apply
to any linear perturbation analysis types. The solution time may be affected depending on the hardware
(processor speed, memory bandwidth, etc.), as well as the chosen element options.
5.2.3. The Jacobi Conjugate Gradient (JCG) Solver
The JCG solver also starts with element matrix formulation. Instead of factoring the global matrix, the
JCG solver assembles the full global stiffness matrix and calculates the DOF solution by iterating to
convergence (starting with an initial guess solution for all DOFs).The JCG solver uses the diagonal of
the stiffness matrix as a preconditioner. The JCG solver is typically used for thermal analyses and is best
suited for 3-D scalar field analyses that involve large, sparse matrices.
For some cases, the tolerance default value (set via the EQSLV,JCG command) of 1.0E-8 may be too
restrictive, and may increase running time needlessly. The value 1.0E-5 may be acceptable in many
situations.
The JCG solver is available only for static analyses, full harmonic analyses, or full transient analyses. (You
specify these analysis types using the commands ANTYPE,STATIC,HROPT,FULL, or TRNOPT,FULL re-
spectively.)
With all iterative solvers, be particularly careful to check that the model is appropriately constrained.
No minimum pivot is calculated and the solver continues to iterate if any rigid body motion is possible.
5.2.4. The Incomplete Cholesky Conjugate Gradient (ICCG) Solver
The ICCG solver operates similarly to the JCG solver with the following exceptions:
- The ICCG solver is more robust than the JCG solver for matrices that are not well-conditioned. Per-
formance varies with matrix conditioning, but in general ICCG performance compares to that of the
JCG solver. - The ICCG solver uses a more sophisticat ed preconditioner than the JCG solver. Therefore, the ICCG
solver requires approximately twice as much memory as the JCG solver.
The ICCG solver is typically used for unsymmetric thermal analyses and electromagnetic analyses and
is available only for static analyses, full harmonic analyses [HROPT,FULL], or full transient analyses
[TRNOPT,FULL]. (You specify the analysis type using the ANTYPE command.) The ICCG solver is useful
for structural and multiphysics applications, and for symmetric, unsymmetric, complex, definite, and
indefinite matrices.
5.2.5. The Quasi-Minimal Residual (QMR) Solver
The QMR solver is used for electromagnetic analyses and is available only for full harmonic analyses
[HROPT,FULL]. (You specify the analysis type using the ANTYPE command.) You use this solver for
Release 15.0 - © SAS IP, Inc. All rights reserved. - Contains proprietary and confidential informationTypes of Solvers