晋太元中,武陵人捕鱼为业。缘溪行,忘路之远近。忽逢桃花林,夹岸数百步,中无杂树,芳草鲜美,落英缤纷。渔人甚异之,复前行,欲穷其林。 林尽水源,便得一山,山有小口,仿佛若有光。便舍船,从口入。初极狭,才通人。复行数十步,豁然开朗。土地平旷,屋舍俨然,有良田、美池、桑竹之属。阡陌交通,鸡犬相闻。其中往来种作,男女衣着,悉如外人。黄发垂髫,并怡然自乐。 见渔人,乃大惊,问所从来。具答之。便要还家,设酒杀鸡作食。村中闻有此人,咸来问讯。自云先世避秦时乱,率妻子邑人来此绝境,不复出焉,遂与外人间隔。问今是何世,乃不知有汉,无论魏晋。此人一一为具言所闻,皆叹惋。余人各复延至其家,皆出酒食。停数日,辞去。此中人语云:“不足为外人道也。”(间隔 一作:隔绝) 既出,得其船,便扶向路,处处志之。及郡下,诣太守,说如此。太守即遣人随其往,寻向所志,遂迷,不复得路。 南阳刘子骥,高尚士也,闻之,欣然规往。未果,寻病终。后遂无问津者。
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# File: tdemo_chaos.py
# Author: Gregor Lingl
# Date: 2009-06-24
# A demonstration of chaos
from turtle import *
N = 80
def f(x):
return 3.9*x*(1-x)
def g(x):
return 3.9*(x-x**2)
def h(x):
return 3.9*x-3.9*x*x
def jumpto(x, y):
penup(); goto(x,y)
def line(x1, y1, x2, y2):
jumpto(x1, y1)
pendown()
goto(x2, y2)
def coosys():
line(-1, 0, N+1, 0)
line(0, -0.1, 0, 1.1)
def plot(fun, start, color):
pencolor(color)
x = start
jumpto(0, x)
pendown()
dot(5)
for i in range(N):
x=fun(x)
goto(i+1,x)
dot(5)
def main():
reset()
setworldcoordinates(-1.0,-0.1, N+1, 1.1)
speed(0)
hideturtle()
coosys()
plot(f, 0.35, "blue")
plot(g, 0.35, "green")
plot(h, 0.35, "red")
# Now zoom in:
for s in range(100):
setworldcoordinates(0.5*s,-0.1, N+1, 1.1)
return "Done!"
if __name__ == "__main__":
main()
mainloop()