problem executing while loop

Question

GreGG 2012-10-9

0
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此问题的直接链接

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采纳的回答： Azzi Abdelmalek

在 MATLAB Online 中打开

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

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GreGG 2012-10-9

在 MATLAB Online 中打开

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)

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Answer 1

Azzi Abdelmalek 2012-10-9

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/50247-problem-executing-while-loop#answer_61345

编辑：Azzi Abdelmalek 2012-10-10

在 MATLAB Online 中打开

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)

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Azzi Abdelmalek 2012-10-9

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

GreGG 2012-10-9

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?

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Answer 2

Sachin Ganjare 2012-10-9

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/50247-problem-executing-while-loop#answer_61346

n should be initialized with proper value, probabaly zero.

Hope it helps

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Answer 3

Amateuromania 2012-10-9

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/50247-problem-executing-while-loop#answer_61347

编辑：Walter Roberson 2012-10-9

在 MATLAB Online 中打开

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)