3.6 PARAMETER FILE Z88I4.TXT FOR THE ITERATION
SOLVER PART 2: Z88I2
Mind the following formats:
[Long] = 4 bytes integer number
[Double] = 8 bytes floating point number, alternatively with or
without point
File only consists of only one line:
1st entry: Number of iterations MAXIT [Long]. When
Z88I2 reaches this value, the solver is halted in any case. The
results reached to this point are printed into Z88O2.TXT, however.
This is the first halt criterion. Enter a value not too small
e.g. 10000.
2nd entry: Limit EPS [Double]. This value is compared
to a norm of the residual vector. When reaching this limit, the
solution may have a good precision. This is the second halt criterion.
Enter a relatively small value, e.g. 0.00001 or 0.0000001. This
are quite proper and tested values. Note that there is no absolute
truth in this field! Which ever norm of the residual vector is
compared against the linit EPS - you can never be sure that all
elements of the solution vector are precise. The choice of
EPS has heavy influence on the iteration count and, thus, on the
computing speed. Remember this when comparing Z88 to the big,
commercial solvers (you don't really know which halt criterions
these folks have programmed). The limits you may adjust in the
commercial solvers may have nothing to do with EPS of Z88. However,
many Z88- tests proved that the deflections of different nodes
compared quite well to those from the commercial solvers if EPS
was between 0.00001 and 0.0000001 with similar elapsed time. And
pay attention to the fact, that you'll never know which solver
delivers the best results when computing a large FEA structure!
3rd entry : Convergence acceleration parameter RP [Double]. Depends on your choice of preconditioner (the solver works with Conjugate Gradients, however).
I recommend SORCG (Conjugate Gradients
with SOR preconditioning) as the default solver, because this
solver needs only about 2/3 of memory of the second solver SICCG
(shifted incomplete Cholesky decomposition, Conjugate Gradients).
Which value may you choose for RP (reads here Omega)
? Good question ! Try RP with 1, this won't result
in too bad results and vary RP for further runs with this FEA
structure.
Example: You want to stop after 5000 iterations, you choose a limit of 0.00001and the convergence acceleration parameter will be 1 for use with SORCG solver.
> Thus: 5000 0.00001 1.