|  | 
| function helix()* i1 n) ~( u' u9 X: `( } % 绘制螺旋线 helical line8 m7 u  p3 V0 m0 L2 a
 % 绘制原理:随着时间的延续或z坐标的升高,
 % q, y: ?2 l0 b4 n% x、y平面上圆的半径不断缩小(指数减小)
 " c$ r8 l% y9 r9 d" mt = 0 : 0.1 : 10 * pi;8 k7 k& N: N- [  P, z# U& X
 x = exp(-t / 20) .* cos(t);
 / z0 K4 _" L7 J# ?/ By = exp(-t / 20) .* sin(t);& Q7 |- O% c4 P$ I6 l
 %z = t;
 " ?/ I7 Y4 R3 K, a. w4 Y% 绘制二维螺旋线
 / \" I9 R; ^3 ?( L: Dfigure
 % U: t0 j! T6 k) ~; Aplot(x, y);* z1 h% H$ P1 c4 |7 W- b# M
 % 绘制三维螺旋线& {8 R0 O, w* ?
 %figure3 f9 p% R- R" [$ ]) h7 N
 %plot3(x, y, z);$ A" T/ G' C& B; [
 return
 & ?3 \8 d4 i- v; y6 s1 ?3 S+ C% W
 | 
 |