polynomials fitting

hi if i want to use polyfit and polyval for two vectores x and y do they must be at the same size?? in my case x is greater than y by one and i want to predict the value of y at that point wt can i do????

Answer 1

[Ben Mitch]

say you have

x = [1 2 3 4];
y = [8 12 16];

then you can fit a polynomial to the region you have data for (the first three samples) using

p = polyfit(x(1:length(y)), y, 1);

and estimate all the samples using

y_est = polyval(p, x);

or just the ones you don't have data for using

y_est = polyval(p, x(length(y)+1:end));