% Samples for institute day 3/10/2006
clc
clf
format compact
p = [1 -2 -7  0 6 2]
p1=polyder(p)
r=roots(p)
r1=sort(roots(p1))
x=linspace(-2,4);
y=polyval(p,x);
x1=linspace(-1.7,1.3);
x2=linspace(3.72,3.76);
y1=polyval(p,x1);
y2=polyval(p,x2);
figure(1)
plot(x,y,[-2,4],[0 0],'k',r',[0 0 0 0 0],'or')
figure(2)
plot(x1,y1,x2,y2,'b',[-2,4],[0 0],'k',r',zeros(1,5),'or')
figure(3)
hold on
x3=linspace(-1.3,0.7);
x4=linspace(2.93,3.0);
y3=polyval(p1,x3);
y4=polyval(p1,x4);
r2=r1(1:3)'
y5=polyval(p,r2);
plot(x1,y1,x2,y2,'b',r',zeros(1,5),'or')
plot(x3,y3,'g',x4,y4,'g',r1',zeros(1,4),'s')
plot([-2,4],[0 0],'k')
plot(r2,y5,'mp')
hold off