Re: NEC-LIST: Could this be a NEC2 bug?

Neoklis,

This is not a bug. NEC-2 is a very old code, and was not written to
be compiled with array bounds checking.
It has been replaced by NEC-4, and is not really supported here any
more. Many arrays whose sizes are set elsewhere, such as those
equivalenced to other arrays or that are passed into subroutines, are
dimensioned (1). In any modern compiler these dimensions could be
replaced by (*) so that bounds checking does not worry about them.
Many of the (1) dimensions in NEC-2 are for model geometry arrays,
and these can be dimensioned to (MAXSEG) for actual bounds checking.
Others are matrix arrays that are most easily dimensioned as (*) or
(NROW,*). The bound is checked in the code. The problem is not
related to the EK command.

However, your model is not valid, since patches are modeled in NEC-2
and NEC-4 with the magnetic field integral equation, and it is valid
only for closed perfectly conducting surfaces. You start with a
single patch and connect a wire to its center so that it splits into
four patches. You would need to use the SM command to make a surface
with more patches, then use other SM or MV commands to form the other
five faces of a closed box. Maybe your file was just meant to
demonstrate the array bounds checking problem, but people often do
use the NEC patch model for non-closed surfaces, and it is completely
invalid. It would be very useful to have a check for non-closed
patch surfaces in NEC-2 or in GUIs written for it , but determining
whether a bunch of patches forms a closed surface is not easy. If
you want to model a monopole on a surface in NEC-2, you should model
the surface as a wire grid.

Also, if you really want to model a wire with length of 1 m and
radius of 0.3 m it would be better to model it as a cage of parallel
wires. You can enter one thin wire offset from the axis of the real
wire on the z axis and spin it around the axis with the GM or GR
commands. If transverse currents on your thick wire are important
you should include circumferential wire segments. Then you would
form a comb-like structure and spin that around. The radii of the
thin wires should be the wire spacing divided by 2*Pi, for the "equal
area rule". Spinning a "L" shaped wire offset from the z axis is an
easy way to form a thick monopole connected to a circular plane.

Regards,
Jerry Burke
LLNL

-- 
The NEC-List mailing list
NEC-List_at_robomod.net
http://www.robomod.net/mailman/listinfo/nec-list