Help with function/script polynom

I'm supposed to make 3 different codes on how to getCoefficient, getplot and getPolynom in matlab. The first line in the getCoeff code is:

function [coeff] = getCoeff(Xp,Yp)

and I know if I've done it right all I should be able to type in

Xp=[1,4,5,6];

Yp=[5,14,21,70];

coeff=getCoeff(Xp,Yp)

it shouldnt matter what degree the polynom is in, the general look is: p(x)= an*x.^n + an-1*x.^n-1+...+a2*x.^2+a1x+a0

how do I put this in a function?

[John D'Errico]

Do you know what polyfit is?

[Sverre]

I typed in:

>> Xp = [1,4,5,6];

>> Yp = [5,14,21,70];

>> p = polyfit(Xp,Yp)

Error using polyfit (line 59) Not enough input arguments.

Don't know why it won't work, I'm new to matlab.. all help is appreciated

[Sverre]

ok I think I figured it out, isntead of typing in

p = polyfit(Xp,Yp)

I typed in:

p = polyfit(Xp,Yp,3)

so I could get the degree the polynom is in.