confusion regarding interp1 command?

Question

ABTJ 2020-6-27

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/555835-confusion-regarding-interp1-command

评论： Star Strider 2020-6-28

I am trying to watch difference between cubic interpolation and spline interpolation using matlab plot but i am getting same plots in both cases using interp1 command

My code is below. In below code ,if i use spline in place of cubic, i still exactly get same plot,why?

clc
clear all
close all
x = 0:pi/4:2*pi; 
v = sin(x);
xq = 0:pi/16:2*pi;
vq2 = interp1(x,v,xq,'cubic');
plot(x,v,'o',xq,vq2,':.');

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Answer 1

Star Strider 2020-6-27

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https://ww2.mathworks.cn/matlabcentral/answers/555835-confusion-regarding-interp1-command#answer_458023

在 MATLAB Online 中打开

The two methods do not produce exactly the same results, however with respect to the amplitude of the values in the plot, they only appear to be the same.

Do this experiment to see how they differ:

x = 0:pi/4:2*pi; 
v = sin(x);
xq = 0:pi/16:2*pi;
vq1 = interp1(x,v,xq,'spline');
vq2 = interp1(x,v,xq,'cubic');
plot(x,v,'o',xq,vq2,':.');
difvct = vq1-vq2;
figure
plot(xq, difvct)
grid