xs=[15, 40, 60, 75];
ys=[0.203,0.377,0.473,0.497];

function y = lagr(x, xs, ys)
y = 0.0;
for k=1:columns(xs)
t = 1.0;
for j=1:columns(xs)
if(j != k )
t=t*((x-xs(j))/(xs(k)-xs(j)));
end
end
y += t*ys(k);
end
end

lagr(20,xs,ys)
lagr(45,xs,ys)
lagr(67,xs,ys)
lagr(85,xs,ys)


step=5;
min=15;
max=75;
x = [min:step:max];
y=x;
for i=1:columns(x)
y(i)=lagr(x(i),xs,ys);
end
plot(x, y);
input(' ');