Based on png-version by User:Jitse Niesen (with gnuplot source code), and on svg-version by User:Cronholm144.

set terminal svg fname "Vera" fsize 25
set output "Interpolation_example_spline.svg"
set key off
set xzeroaxis
set xtics axis 1,1
set ytics nomirror 1
set samples 300
set border 2
f(x) = (x >= 0 && x < 1) ? -0.1522*x**3 + 0.9937*x : \
       (x >= 1 && x < 2) ? -0.01258*x**3 - 0.4189*x**2 + 1.4126*x - 0.1396 : \
       (x >= 2 && x < 3) ? 0.1403*x**3 - 1.3359*x**2 + 3.2467*x - 1.3623 : \
       (x >= 3 && x < 4) ? 0.1579*x**3 - 1.4945*x**2 + 3.7225*x - 1.8381 : \
       (x >= 4 && x < 5) ? 0.05375*x**3 -0.2450*x**2 - 1.2756*x + 4.8259 : \
                           -0.1871*x**3 + 3.3673*x**2 - 19.3370*x + 34.9282 
set yrange [-1.1:1.1]
plot f(x) with lines linetype 3 linewidth 4, \
     "-" with points linetype 1 pointtype 7 pointsize 0.7,\
	 0 with lines linetype -1 linewidth 1
0 0
1 0.8415
2 0.9093
3 0.1411
4 -0.7568
5 -0.9589
6 -0.2794
e

Please use at least version 4.2 of Gnuplot for smooth lines in SVG.

This work has been released into the public domain by its author, I, Berland. This applies worldwide. In some countries this may not be legally possible; if so: I, Berland grants anyone the right to use this work for any purpose, without any conditions, unless such conditions are required by law.