clear, clc

x=[0.0,0.2,0.3,0.5]; 
y=[0.0,0.18,0.26,0.41]; 

X=0.0:0.01:0.5;
Y=interp1(x,y,X); 
Y1=interp1(x,y,0.1); 
Y2=interp1(x,y,0.4); 
%Y3=interp1(x,y,0.8); 

plot(x,y,'r*',X,Y)
hold on
plot(0.1,Y1,'bo')
plot(0.4,Y2,'bo')
%plot(0.8,Y3,'bo')

hold off