[slgu]

请见该例：
x=[38.8490, 37.7060, 31.1880, 20.2380, 6.86600, -6.59400, -18.0560, -26.1350, -30.3280, -30.8140, -28.0350, -22.5420, -14.7820, -5.25900, 5.47500, 16.5870, 26.8930, 34.8520];
y=[ 0., 13.7240, 26.1070, 35.0530, 38.9340, 37.4020, 31.2760, 21.9310, 11.0390, .1000e-2, -10.2040, -18.9150, -25.6030, -29.8250, -31.0490, -28.7290, -22.5650, -12.6840];
b=[35.06010729, 4.016838807, .2587265862e-2]
x1=linspace(min(x)-1,max(x)+.5,120);
y1=sqrt(b(1)*b(1)-(x1-b(2)).^2)+b(3)+4;
plot(x,y,'o','markerfacecolor','k','markeredgecolor','k','markersize',8)
hold on
plot(x1,y1,'b-','linewidth',3)
y2=-sqrt(b(1)*b(1)-(x1-b(2)).^2)+b(3)+4;
plot(x1,y2,'b-','linewidth',3)
plot(b(2),4+b(3),'or','markerfacecolor','r','linewidth',2)
axis tight