how can we plot our 4th order polynomial with given data by using polyfit and polyval ?

x=[0.1 0.2 0.4 0.6 0.9 1.3 1.5 1.7 1.8];

y=[0.75 1.25 1.45 1.25 0.85 0.55 0.35 0.28 0.18];

n=9;

figure

pfit4=polyfit(x,y,4);

plot(x,y,'ro')

hold on

grid on

plot(x,pfit4,'g-')

hold off

title('polyfit table')

figure

pval4=polyval(x,y,4);

plot(x,y,'ro')

hold on

grid on

plot(x,pval4,'g-')

hold off

title('polyval table')

Answer 1

[Star Strider]

You have the correct idea, and correct code except for the polyval call.

Try this:

x=[0.1 0.2 0.4 0.6 0.9 1.3 1.5 1.7 1.8];
y=[0.75 1.25 1.45 1.25 0.85 0.55 0.35 0.28 0.18];
pfit4=polyfit(x,y,4);
pval4=polyval(pfit4,x,4);

figure
plot(x,y,'ro')
hold on
plot(x,pval4,'g-')
hold off
title('polyval table')

That should do what you want: