Compute polynomial coefficient with unequal vector?

Hello all, I have question about to compute polynomial coefficient with unequal number of membership of 2 vectors. If I have vector A as 10x1 and vector B as 7x1, can I possibly compute coefficient with order 4 of this 2 vectors? Thanks Ani.

[KSSV]

A fourth order polynomial has five unknowns..you have seven points known..you should be able to do it eh.

[AniCnx]

On polyfit of matlab, it needs equally membership of vector A and B. Do it has any built in function of that problem?

Answer 1

[KSSV]

%%a random data
x = rand(10,1) ;
y = rand(7,1) ;
% sort x in ascending order and pick first seven 
x = x(1:7) ;
%
[x,idx] = sort(x) ;
y = y(idx) ;

%%fit fourth order polymomial
[P,S] = polyfit(x,y,4) ;

x1 = linspace(min(x),max(x));
y1 = polyval(P,x1);

figure
plot(x,y,'-or')
hold on
plot(x1,y1)
hold off

[AniCnx]

thank you very much, KSSV. I have some question from 'pick first seven', so that means it still need to be equal membership of the two vector, is that right? If I pick the last seven, coefficient will be changed from the first seven, am I corrected?

[KSSV]

Yes...

[AniCnx]

Thank you very much, KSSV. May I ask one more question? That I have A=10x1, B=7x1. If I re-sampling B to be C=10x1. Coefficient of AB is equal or not equal to AC?