Functions and For Loops For Polynomials

I need to write a function that takes two inputs, a vector that is the the coefficients of a polynomial starting with the lowest degree term and a scalar to evaluate it at, I'm supposed to use a for loop to evaluate it in the function. I also cannot use '^' this built in function. Any guidance?

[James Tursa]

What have you done so far? What specific problems are you having with your code?

[Alex Baham]

This is what I have so far, but I'm not sure how much really needs to go in the for loop.

function y = arbpoly2(c,x)
n = length(c)-1;
r=n:-1:0;
for i=1:n
    sum=0
    sum=sum + c*x

Answer 1

[James Tursa]

Some guidance:

1) The sum=0 part needs to be moved outside the loop, prior to the loop starting. The way you have it the sum resets to 0 at each iteration.

2) Don't use "sum" as a variable name since that is an important existing MATLAB function name. Use something else, like "mysum" instead.

3) c is a vector of coefficients, so you should be indexing into c inside your loop. E.g., c(i)

4) The x needs to have an exponent applied to it based on the index i.

Make an attempt at these fixes and come back with any more problems you are having.

[Alex Baham]

Will do. Thanks!

Answer 2

[David Hill]

Too bad you can't use polyval(). This might get you started.

function e=evalPoly(p,a)
x=1;
e=0;
for k=1:length(p)
    e=e+p(k)*x;
    x=x*a;
end