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馈电点如果不是导线的起点、中心、终点，怎么设置？
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里面的帮助有说明的，自己试多几次就知道馈电点在哪了。
sources (feeding point)
pulse ?pulse position
phase ?phase of feeding
voltage ?voltage of feeding
use the following convention for defining pulse positions. w#c(#)
offset from the center of the wire
w#b(#)
offset from the beginning position of the pulse assignment on the wire
w#e(#)
offset from the ending position of the pulse assignment on the wire
example :
w1c
center of wire 1
w3c1
one point ahead of the center of wire 3
w2c-2
two points behind of the center of wire 2
w2b
the beginning position of wire 2
w5e3
three points behind of the ending position of wire 5
