Finding the root of a real number using Newton-Raphson Method [Homework Help]

I'm working on this project for school that requires me to find the real root of a number using the Newton Raphson Method (equation given is x1 = 0.5 * (x + (R/x)). Here is my code:

   R=10;
   x=3;
    iter = 0;
    max_iter = 10;
    perc_tol = 5;
    answer = 0;

    while iter < max_iter || answer > perc_tol
        x = (0.5*(x+(R/x)));
        no_iter = no_iter + 1;
        answer = ((abs((x1-x)/(x1)))*100);
    end

    disp(x1)
    disp(iter)

The problem I keep getting is it becomes an infinite loop (because the answer never becomes <= perc_tol I assume) and if I keep only the 'iter < max_iter' then it only performs the loop once , no matter the defined number of iterations. Any suggestions?

Answer 1

[Walter Roberson]

      while no_iter < max_iter && answer > perc_tol

By the way, what is the xinew that you

      disp(xinew)

[Fraser Fife]

xinew = x1 and no_iter = iter, just changing the variable names from my code as they need to be stupidly long for the hand in.

When I change it to && my I get the error that "x1 is undefined in line 14" ('disp(xinew)')

[Walter Roberson]

How can you be getting an error about x1 being undefined on a line that contains no reference to x1 ?

We need the real code and the real error messages.

[Fraser Fife]

Code:

R=10;
xi=3;
no_iter = 0;
max_iter = 10;
perc_tol = 5;
answer = 0;

while no_iter < max_iter && answer > perc_tol
    xinew = (0.5*(xi+(R/xi)));
    no_iter = no_iter + 1;
    answer = ((abs((xinew-xi)/(xinew)))*100);
end

disp(xinew)
disp(no_iter)

Error:

Undefined function or variable 'xinew'.

Error in a4_test2b (line 14)
disp(xinew)

[Walter Roberson]

You start with answer = 0 and you test it against perc_tol which is 5. 0 > 5 is false so your loop body is not run even once.

Suggestion: initialize answer to infinity.