ex3_33.m

华东理工大学自动化系《控制系统分析、设计和应用》教材配套程序实例,有关说明： 1. 安装MATLAB软件。安装时

% ex3_33
% 等倾线法绘制二阶系统的相平面图
figure('pos',[50,50,300,300],'color','w');
axes('pos',[0.14,0.14,0.75,0.75]);
for j=1:4; 
    x(1)=0;
    dx(1)=j; 
    alf(1)=-x(1)/dx(1)-1;
for i=[1:1000]; 
    alf(i+1)=alf(i)-0.1;
    as(i)=(alf(i)+alf(i+1))/2;
    x(i+1)=-(dx(i)-as(i)*x(i))/(as(i)+1/(1+alf(i+1))); 
    dx(i+1)=-1/(1+alf(i+1))*x(i+1);
    line([x(i) x(i+1)],[dx(i) dx(i+1)]);
    hold on;
end;
xx(1)=x(1001);
dxx(1)=-dx(1001);
al(1)=-xx(1)/dxx(1)-1;
for i=[1:1000]; 
    al(i+1)=al(i)-0.1;
    asl(i)=(al(i)+al(i+1))/2;
    xx(i+1)=-(dxx(i)-asl(i)*xx(i))/(asl(i)+1/(1+al(i+1))); 
    dxx(i+1)=-1/(1+al(i+1))*xx(i+1);
    line([xx(i) xx(i+1)],[dxx(i) dxx(i+1)]);
end;
x2(1)=xx(1001);
dx2(1)=dxx(1001);
al2(1)=-x2(1)/dx2(1)-1;
for i=[1:1000]; 
    al2(i+1)=al2(i)-0.1;
    asl2(i)=(al2(i)+al2(i+1))/2;
    x2(i+1)=-(dx2(i)-asl2(i)*x2(i))/(asl2(i)+1/(1+al2(i+1))); 
    dx2(i+1)=-1/(1+al2(i+1))*x2(i+1);
    line([x2(i) x2(i+1)],[dx2(i) dx2(i+1)]);
end;
end;
line([0 0],[-2 4],'lines',':');
line([-0.5 2.5],[0 0],'lines',':')
axis([-0.5 2.5 -2 4]);
set(gca,'box','on')