# Help: Smooth a curve generated from a group of specified points

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Khanh on 18 Sep 2014
Commented: Star Strider on 19 Sep 2014
Hi,
I have 2 vector of x, y coodinates of points
x=[0 50 935 1870 1935 2805 3740 4675 5610 6545 6746 7480 7911 8415 8590 9004];
y=[300 600 716 892 900 990 1052 1071 1037 934 900 736 600 393 300 0];
length(x)=length(y)=16.
The first curve is generated by plot(x,y).
Because I want to smooth the orginal curve. From x, y vectors, I want to generate x', y' vectors with length(x')=length(y')=101. And the second curve is generated by plot(x',y').
I also created a script to do it, but the result wasn't same as the one I want.
My script:
clc
clear all
x=[0 50 935 1870 1935 2805 3740 4675 5610 6545 6746 7480 7911 8415 8590 9004];
y=[300 600 716 892 900 990 1052 1071 1037 934 900 736 600 393 300 0];
plot(x,y,'-o');
xnew=linspace(x(1),x(end),101);
ynew=spline(x,y,xnew);
figure
plot(xnew,ynew,'--o');
The curve generated by plot(x,y):
The curve generated by plot(x',y'):
The result I want to get:
Khanh.

Star Strider on 18 Sep 2014
Using interp1 with the 'pchip' method will get you closer:
xi = linspace(min(x),max(x),101);
yi = interp1(x, y, xi, 'pchip');
figure(1)
plot(x, y, '+r')
hold on
plot(xi, yi)
hold off
grid
I experimented with resample, even though it is intended for signal processing. It is definitely not appropriate here.
##### 2 CommentsShow 1 older commentHide 1 older comment
Star Strider on 19 Sep 2014
My pleasure!

Salaheddin Hosseinzadeh on 18 Sep 2014
Hello Khanh, Please try to use resample rather than spline
doc resample
Simply resample your x and y value with same factor and then plot them.
Good Luck!
Khanh on 19 Sep 2014
Thanks.