NEC-LIST: compute time & RAM allocation

Hi-
Is there a way to calculate computation time and/or memory
requirements in advance of simulation? I'm particularly interested in
the requirements for electrically small geometries of variable extent,
near earth-ground, and using the Sommerfeld-Norton approximation.

Backstory:
  After discovering that NEC simulations fail when wires overlap, I
wrote a script that creates my desired input geometry from up to 100k
wires. Ultimately, I'm interested in simulating the affect on antenna
response due to the addition of a ground screen. Some of the possible
candidates for ground screens have dimensions well below the
definition of electrically small; that is, the grid spacings are much
less than 0.1*wavelength. I've read a bit of the NEC manual, and I
realize that the approximations made by NEC are less accurate in this
regime. (My thinking is that inaccurate simulation yields more
information than no simulations.)
  The problem that I'm having is that I don't completely understand the
memory and time requirements for the method of moments calculations.
As I understand it, time for LU decomposition should go like
(segments)^3. Since the number of segments is large -- the number of
segments is large even if the wires aren't split into smaller segments
for matrix inversion-- I would expect this matrix inversion to be the
dominant time requirement. However, there appears to be some larger
effect due to the extent of the geometry. For example, an antenna over
a square ground screen with sides of 3m, composed of about 70k wires,
takes several times 10^3 minutes, using 2GB of RAM for the duration of
the simulation. For the same grid spacing, a screen larger in extent
by a factor of ten simulates in less than eight minutes, and uses tiny
amounts of memory. For calculating time of computation and memory
allocation, I'd really like to get some information on the finer
details of NEC, and it's benchmark testing.

thanks in advance
-Billy Robbins

-----------------------------------------------
W.J. Robbins
Naval Research Lab., Code 7655
4555 Overlook Avenue, SW
Washington, DC 20375
Tel. + 202.404.7196
Cell. + 805.624.6744
Fac. + 202.767.0497
Skype: wjrobbins2

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