求帮忙求一下x1和h的幅频特性曲线，初始值随便取，谢谢啊...
ms=200; 
ks=30000;
mu=40;
Fm=200;
kt=181000;
c0=1000;
B=100;
h=1;
%FM=(Fm*(1-exp(-B*(x(2)-x(4))))/(1+exp(-B*(x(2)-x(4)))));
xr=0.01*sin(2*pi*h*t);

dx=[
    x(2)
    -ms^(-1)*(ks*(x(1)-x(3))+c0*(x(2)-x(4))+Fm*(1-exp((-B)*(x(2)-x(4))))/(1+exp((-B)*(x(2)-x(4)))))
    x(4)
    mu^(-1)*(ks*(x(1)-x(3))+c0*(x(2)-x(4))-kt*(x(3)-xr)+Fm*(1-exp((-B)*(x(2)-x(4))))./(1+exp((-B)*(x(2)-x(4)))))
    ];