problem executing while loop

im writing a script to solve the square root of a number using halley's method

my equations: y=(1/a)*x^2

n = (x/8)*(15-(y)*(10-3*(y)))

then n becomes the new x and the equation repeats

my problem is its not looping it runs through once and then stops

clc
clear
a = input('number ');
x = input('guess ');
tol = 0.0000001;

while (abs(n-x)<=tol)
y=(1/a)*x^2;
n = ((x/8)*(15-(y)*(10-3*(y))));
x=n;
end
disp(n)

i want the loop to stop when the number is accurate to 6 decimal places. what am i doing wrong

very new to ML

[GreGG]

ended up figuring it out

clc
clear
a = input('number ');
x = input('guess ');
tol = 0.000001;
dif=inf;
while dif>=tol
    y=(1/a)*x^2;
    n = ((x/8)*(15-y*(10-3*y)));
    dif= (abs(n-x));
    disp(n)
    x=n;

end
disp(n)

Answer 1

[Azzi Abdelmalek]

insert before while n=x;

clc
clear
a = input('number ');
x = input('guess ');
tol = 0.0000001;
n=x
while (abs(n-x)<=tol)
y=(1/a)*x^2;
n = ((x/8)*(15-(y)*(10-3*(y))));
x=n;
end
disp(n)

[GreGG]

when i do that the code never enters the loop it just displays 1.0e^-7

am i using the absolute value comand right?

[Azzi Abdelmalek]

No, it enter the loop once, check the value of x. t's changed de tol. The problem is in your code, or it depends on the value of a and x

[Azzi Abdelmalek]

initialize n to x

 n=x

[GreGG]

now i get an infinite loop

[Azzi Abdelmalek]

does'nt mean there is an error in your code.

[Azzi Abdelmalek]

but if you want to quit a loop after a certain number of itteration, we can add another condition

[GreGG]

eventually i want to adjust the code so that the user can decide how many accurate decimal places they get each loop adds 2 correct decimals (or something like that i dont remember right now)...am i on the right track for this?

Answer 2

[Sachin Ganjare]

n should be initialized with proper value, probabaly zero.

Hope it helps

Answer 3

[Amateuromania]

You haven't declared n. First calculate n then check the condition much like the do while loop.

You can use something like this:

clc;
clear;
a = input('number ');
x = input('guess ');
tol = 0.0000001;
y=(1/a)*x^2;
n = ((x/8)*(15-(y)*(10-3*(y))));
x=n;
while (abs(n-x)<=tol)
  y=(1/a)*x^2;
  n = ((x/8)*(15-(y)*(10-3*(y))));
  x=n;
end;
disp(n)