无阻尼二自由系统固有频率的程序

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% 无阻尼二自由系统固有频率的程序 20180401A
m1=100;m2=100;k1=200;k2=400;%
$ r; ?' k4 [* W0 N3 A. z2 C9 I5 \c1=0;c2=0;
x0=[1;0];xd0=[0;0];tf=50;dt=0.1;
. z9 `: Y" c+ D0 u0 eM=[m1,0;0,m2];k=[k1+k2,-k2;-k2,k2];
  b' E) V- m1 Z3 Bc=[c1+c2,-c2;-c2,c2];
; R- M- e; l4 z3 y6 \A=[zeros(2,2),eye(2);-M\k,-M\c];
y0=[x0;xd0];
for i=1:round(tf/dt)+1
1 v3 z9 \% n9 m    t(i)=dt*(i-1)
    y(:,i)=expm(A*t(i))*y0;
( ~) s9 C. @( send
* U  L* V8 Y; }: m$ `+ Wsubplot(2,1,1),plot(t,y(1,),grid  
subplot(2,1,2),plot(t,y(2,),grid
[p,lamda]=eig(A)
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& J+ B* g7 l: T  y  r
lamda =
  Columns 1 through 2
  0.000000000000000 + 3.020447918044219i  0.000000000000000 + 0.000000000000000i
" l) S' g; I5 @  L/ ]; i8 U  0.000000000000000 + 0.000000000000000i  0.000000000000000 - 3.020447918044219i
: J/ S. ^+ E! W, [2 ]. [  0.000000000000000 + 0.000000000000000i  0.000000000000000 + 0.000000000000000i
  0.000000000000000 + 0.000000000000000i  0.000000000000000 + 0.000000000000000i
  Columns 3 through 4
# _& X: }3 `+ w  C/ S  0.000000000000000 + 0.000000000000000i  0.000000000000000 + 0.000000000000000i
& F: H; H$ g: o2 L. G  0.000000000000000 + 0.000000000000000i  0.000000000000000 + 0.000000000000000i
- {2 |) l0 k* U" I( x0 b -0.000000000000000 + 0.936426384924271i  0.000000000000000 + 0.000000000000000i
  0.000000000000000 + 0.000000000000000i -0.000000000000000 - 0.936426384924271i
4 S& u+ t1 {+ K! y
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鸿鹄重工

代码中有个笑脸是啥意思，此处应该是什么代码？