newton method code with user input

HI, I have simple problem, Iam trying to use newton's method with the code below. However since my polynomial is always going to be in fourth order I wish to make it a user input method to make it easier for myself rather than having to write the 100+ polynomials.

    % code
function p=test(x)
a1=input('Type a1 value:  \n');
a2=input('Type a2 value:  \n');
a3=input('Type a3 value:  \n');
a4=input('Type a4 value:  \n');
p=1+a1*x+a2*x^2+a3*x^3+a4*x^4;
z=diff(f(x));
f1=inline(z);
x0=input('Guess the number= \n');
x=x0
for u=0:inf
    y=x
    x=y-(f(x)/f1(x));
    if x==y
        break
    end
end

I will greatly appreciate your help.
thanks

[Ced]

I am not sure I understand the question. Why would you have to write 100+ polynomials? Why not just pass the coefficients as a input parameter to your function, i.e.

function p = test(x,a)
% a = [ a0 a1 a2 a3 a4 ]

p = x.^(0:5)*a(:); % this does 1*a0 + x*a1 + ... + x^4*a4

...

Otherwise, you can also pass a complete vector with input:

a = input('Type the coefficient vector [ a0 a1 a2 a3 a4 ]\n');

Then, minor comments:

1. I would recommend using a finite maximum number of iterations instead of inf.

2. You will probably want to check (abs(x-y) < small_number) instead of x == y since this is a numerical algorithm.

PS: You might want to have a look at polyval if you want to use inbuilt matlab functions with polynomials