cubic ploynomial fitting problem

Hi,

I have 8 points ina data file on which m fitting cubic polynomial.. when i do fitting using cftool den i get a smooth fitting curve..

but if i use polyfit and polyval commands and plot then the fit curve is not that smooth.. how can i get a similar fitting curve like i get in cftool...

plz anybody help me with it

[dpb]

Have to see what actually did -- was it the same data?

[John D'Errico]

As those who answered this have said, you must use more then 8 points to plot. Otherwise, plot just does connect-the-dots with straight line segments.

Answer 1

[Matt J]

Try plotting the curve at more than 8 points, e.g., 1000.

Answer 2

[Star Strider]

If x and y are your data:

x = ...
y = ...
p = polyfit(x,y,3);                      % Fit data

xp = linspace(min(x), max(x), 200);      % Create 200 points linearly-spaced in x

yfit = polyval(p, xp);

Then plot your data as (x,y) and the fit as (xp,yfit).