Cubic Spline method for extrapolation in MatLab -

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i'm trying predict value @ next time step of sinusoidal waveform. i'm using cubic spline extrapolation found in web page.

http://mathworld.wolfram.com/cubicspline.html

the following matlab code used.

clear all;close  v0_mag=230*sqrt(2/3);  t1=0;dt=50e-6;  h=dt;  h=[4 1 0;1 4 1;0 4 1];  invh=inv(h);  y = zeros(3,1);  w0=2*pi*60;a=0;b=0;c=0;d=0;  t=1; m=1:0.2/dt     t11(m)=t1;     y(m,1)=v0_mag*(1-exp(-20*t11(m)))*sin(w0*t11(m));     %cubic splines method n=3     if m>5         y(3,1)=3*(y(m-2)-y(m-3));     end     if m>4         y(3,1)=3*(y(m-1)-y(m-2));     end     if m>3         y(3,1)=3*(y(m)-y(m-1));     end     d=(invh*y);     ax(m)=a;     if m>1         a=y(m-1);b=d(2);         c=3*(y(m)-y(m-1))-(2*d(2)+d(3));         d=2*(-y(m)+y(m-1))+d(2)+d(3);     end     prey1(m,1)=d*(t)^3+c*(t)^2+b*(t)+a;     t1=t1+dt; end  figure(1) plot(t11,prey1) hold on plot(t11,y,'r') legend

this code works 0<t<1(interpolation). extrapolate have make t>1. , when put t=2 (that means i'm trying find value @ next time step) waveforms not match. can me how extrapolation using code.


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