function bstep(Bsys,wcha)
global p n C1 C2 Cinf Mp tp tr Ts y t windstep
[bnum,bden]=tfdata(Bsys,'v');n=length(bnum);
for i=1:n
    if bnum(i)==0
        bnum1=bnum(i+1:n);
    else
        clear bnum;bnum=bnum1;break
    end
end
p=roots(bden);ii=find(p>=0);n=length(ii);
if(n>0),disp('system is Unstable');
    dcgwdisp=['系統不穩定！'];
   helpdlg(dcgwdisp,'時域指標');break;
else,disp('system is stable');                  % 判斷閉環系統的穩定性
t=0:0.1:5000;                                  % 設置系統響應的時間間隔范圍
% 計算閉環系統階躍響應的參數
[y,x,t]=step(bnum,bden,t); n=length(t); Cinf=y(n);   % Cinf為穩態終值
C1=Cinf+Cinf*wcha;C2=Cinf-Cinf*wcha;         % C1,C2為上下誤差帶的兩個值
    u1=find(C1<y);u2=find(C2>y);            % u1為小于C1計算值集合下標的向量；
                                          %u2為大于C2計算值集合下標的向量
    u3=max(u1);u4=max(u2);    % u3和u4分別為向量中的最大值，即為階躍響應輸出
                             %向量y中的元素進入上下誤差帶的最大下標值。
    if u3>=u4,i=u3;            % 判斷出u3，u4的最大值，并賦值給i
    else
      i=u4;
    end
Ts=t(i);                          % 調節時間
Mp=max(y);                      % 最大超調量
tn=find(y==Mp);
tp=t(tn);
screen=get(0,'screensize');
winw=screen(3);winh=screen(4);
l8='系統輸出Y(t)之單位階躍響應;  誤差帶=';l9=num2str(wcha*100);l7='%';
l10=[l8,l9,l7];
windstep=figure('color',[1,1,1],'position',[0.1*winw,0.1*winh,0.8*winw,0.8*winh],...
       'name',l10,'numbertitle','off','menubar','figure',...
       'resize','off');
step(bnum,bden)                % 階躍響應的圖形
hold on
plot([tp,tp],[0,Mp],'k:')
plot([Ts,Ts],[0,y(i)],'k:')
plot([0,t(n)],[C1,C1],'r:')
plot([0,t(n)],[C2,C2],'r:')
text(tp,Mp,'Mp')
text(tp,0,'Tp')
text(Ts,0,'Ts')
syms s
  %sys=tf(bnum,bden);[bnum,bden]=tfdata(sys,'v');
  [numlength1 numlength2]=size(bnum);
  [denlength1 denlength2]=size(bden);
  l1=['('];
  for i=1:numlength2-1
     l1=[l1 num2str(bnum(1,i)) '*s^' num2str(numlength2-i) '+'];
  end;
  l1=[l1 num2str(bnum(1,numlength2)) ')'];
  l2=['('];
  for i=1:denlength2-1
     l2=[l2 num2str(bden(1,i)) '*s^' num2str(denlength2-i) '+'];
  end;
  l2=[l2 num2str(bden(1,denlength2)) ')'];
  l3=[l1 '/(' l2 ')'];
  title(l3) 
uicontrol(windstep,'style','push','string','穩態值',...
       'position',[0.06,0.01,0.11,0.05],'units','normalized',...
      'callback','re_dcg');
uicontrol(windstep,'style','push','string','上升時間tr',...
       'position',[0.22,0.01,0.11,0.05],'units','normalized',...
      'callback','re_tr');
uicontrol(windstep,'style','push','string','峰值時間tp和最大超調量Mp',...
       'position',[0.37,0.01,0.25,0.05],'units','normalized',...
      'callback','tpmp');
uicontrol(windstep,'style','push','string','調整時間ts',...
       'position',[0.66,0.01,0.11,0.05],'units','normalized',...
      'callback','re_ts');
uicontrol(windstep,'style','push','string','結束',...
       'position',[0.83,0.01,0.11,0.05],'units','normalized',...
      'callback','fclosestep');
  end