For some applications the system of equations must be solved several times. This frequently occurs in nonlinear analysis where the matrix coefficients Aij depend on the value of the solution vectors {X}. When this occurs significant computation can be saved by starting the second and subsequent solutions at the first changed equation. It is not necessary to know which equations will be changed during the current solution. This information is not available until the solution is completed and the values of {X} are known.

After the first solution is completed, the FMS Parameter LOWASM is used to specify the first equation in the matrix which has a term which changed. The next solution will skip all computation below this value of LOWASM. By properly locating the equations containing nonlinearities at the bottom of the matrix, you may save a significant amount of computation. The value of LOWASM can change with each solution.

LOWASM

The original matrix and factored matrix data must be kept on separate files. The new matrix data, starting at LOWASM, is used to update the original matrix file. During factoring FMS will round the value of LOWASM down to start on a segment boundary. This prevents records from containing a mix of factored and unfactored data. After the factoring process the original matrix file and the factored matrix file will be based on the current values.

One benefit of this feature is that you do not need to know the restart point in advance when the matrix [A] is factored the first time. You simply determine LOWASM as you are processing the solution {X} and FMS automatically skips the appropriate calculations on the next solution.

For example, in a structural finite element analysis, this feature would be used as follows:
  1. Initialize your value of LOWASM to 1 greater than the number of equations.
  2. Loop over the elements. Use the displacements {X} from the previous solution to compute new values of strains and stresses.
  3. If nonlinear effects are observed due to large deformations or material nonlinearities, set LOWASM=MIN0(LOWASM,ILOW), where ILOW is the lowest equation in the element. 
  4. CALL FMSIST('LOWASM',LOWASM)
    to pass your value of LOWASM to FMS.

This parameter may also be used to recover a factoring process that terminates prematurely. During the initial factoring, set the FMS Parameter IREST to write the restart data. On the second (recovery) run, set this FMS parameter LOWASM to the highest factored segment (or slab) printed by FMS during the first run.