confusion regarding interp1 command?

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,':.');

Answer 1

[Star Strider]

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

.

[ABTJ]

so which type of interpolation is better?spline or cubic?

[Star Strider]

It likely does not matter. They are almost the same, nowever not actually the same. That was the oint of my post.

I usually use 'pchip' if I want something other than 'linear'.