3.6 PARAMETER FILE Z88I4.TXT FOR
THE SPARSE MATRIX SOLVERS PART 2: Z88I2 AND Z88PAR
Mind the following formats:
[Long] =
4 bytes or 8 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 limit 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 ALPHA [Double].
This
parameter for the SIC pre-conditioner
of Z88I2 defines the Shift factor ALPHA (from 0 to 1, good values may
vary from 0.0001 to 0.1. For further
information consult the special literature)
4th entry: Convergence
acceleration parameter OMEGA [Double].
This
parameter for the SOR pre-conditioner
of Z88I2 defines the
Relaxation factor OMEGA (from 0 to 2, good values may
vary from 0.8 to
1.2.
How to
choose OMEGA ? Good question! Try 1.0 for
a first start and try other values for
further Z88 runs with this structure.
5th entry: Z88PAR: number of cores
or CPUs on multi-core computers. A maximum number of 9 is allowed.
Example
1:
You want to stop
after 5000 iterations, you choose a limit of 0.0000001 and
the convergence acceleration parameter OMEGA will be 0.9 for use with SORCG
solver.
>
Thus: 5000
0.0000001 0.001
0.9 1
Example
2: You want
to use the Sparse Matrix Iteration Solver Z88I2. You want to
stop positively after 10000 iterations, the limit shall be 10-9
and
the Shift factor ALPHA for
SIC shall be 0.001 because
you want to use the SIC pre-conditioner.
>
Thus: 10000
1e-9 0.001 0.9
1
Example 3: You want to use the direct
Sparse Matrix Solver with
fill-in Z88PAR and you have two double core CPUs in your computer
installed.
>
Thus:
10000 1e-9
0.001
0.9 4
The not-underlined entries
have no meaning for Z88PAR.