cubic ploynomial fitting problem

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aditi
aditi 2014-5-26
评论： John D'Errico 2014-5-26
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
  2 个评论
dpb
dpb 2014-5-26
Have to see what actually did -- was it the same data?
John D'Errico
John D'Errico 2014-5-26
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.

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回答（2 个）

Matt J
Matt J 2014-5-26
Try plotting the curve at more than 8 points, e.g., 1000.
Star Strider
Star Strider 2014-5-26
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).

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