Matrices are reused automatically as often as possible in order to decrease running time. The information below is made available for use in running time estimates.
For static (ANTYPE,STATIC) or full transient dynamic (ANTYPE,TRANS with TRNOPT,FULL) analyses, element stiffness/conductivity, mass, and damping/specific heat, matrices ([Ke], [Me], [Ce]) are always reused from iteration to iteration, except when:
The full Newton-Raphson option (NROPT,FULL) is used, or for the first equilibrium iteration of a time step when the modified Newton-Raphson option (NROPT,MODI) is used and the element has either nonlinear materials or large deformation (NLGEOM,ON) is active.
The element is nonlinear (e.g. gap, radiation, or control element) and its status changes.
MODE or ISYM (MODE command) have changed from the previous load step for elements PLANE25, SHELL61, PLANE75, PLANE78, or PLANE83.
will be reformulated if a convective
film coefficient (input on the SF or SFE commands) on an element face changes. Such a change could occur
as a ramp (KBC,0) within a load step. The materials or real constants are changed by new input, or if the material properties have changed due to temperature changes for temperature-dependent input.
Element stress stiffness matrices [Se] are never reused, as the stress normally varies from iteration to iteration.
The overall structure matrices are reused from iteration to iteration except when:
An included element matrix is reformed (see above).
The set of specified degrees of freedom (DOFs) is changed.
The integration time step size changes from that used in the previous substep for the transient (ANTYPE,TRANS) analysis.
The first iteration of a restart is being performed.
The above tests are all performed automatically by the program. The user can select to override the program's decision with respect to whether the matrices should be reformed or not. For example, if the user has temperature-dependent input as the only cause which is forcing the reformulation of the matrices, and there is a load step where the temperature dependency is not significant, the user can select that the matrices will not be reformed at that load step (KUSE,1). (Normally, the user would want to return control back to the program for the following load step (KUSE,0)). On the other hand, the user can select that all element matrices are to be reformed each iteration (KUSE,-1).