need help for transfer Whlile loop from For loop

two newton method written with for and while loop.

the result is quite different

where should i fix it?

big thx from bottom of my heart.

Answer 1

[Sindar]

First issue:

• for loop ends when error<tol
• while loop continues when error<tol

[pepper]

got it after fix the side of the <,>

trapped in infinite loop..

any thoughts sir?

[Sindar]

can you comment your current code, in a comment block (not a screenshot)? But, similarly to the first issue, think about what is happening during the for/while loops, versus what happens before each loop - is it consistent?

[pepper]

function p1=newton(ex31,a)

tol=10^-10;

a=5;

p0=2;

for k=1:1000

p1=1/2*(p0+a/p0);

error=abs((p1-p0)/p0);

p0=p1;

if error<tol

p=p1;

break

end

end

-------------------------------------------------

i slightly changed value to pn and it run ok !

one thought in my mind is ,

is it possible that i make it run ok with the first one?(above one)

kinda lacked if i use p1,p0 value

function p1=newton(ex31,a)

tol=10^-4;

error=1.0;

p0=2;

pn=p0;

a=5

while error>tol

pn1=1/2*(pn+a/pn);

error=abs(pn1-pn)/abs(pn1-p0);

pn=pn1;

end

pn1

i don't understand about your consistent means.

[Sindar]

switching between text and code blocks helps readability

"for"

function p1=newton(ex31,a)
tol=10^-10;
a=5;
p0=2;
for k=1:1000
    p1=1/2*(p0+a/p0);
    error=abs((p1-p0)/p0);
    p0=p1;
    if error<tol
        p=p1;
        break
    end
end

"while"

function p1=newton(ex31,a)
tol=10^-4;
error=1.0;
p0=2;
pn=p0;
a=5
while error>tol
      pn1=1/2*(pn+a/pn);
      error=abs(pn1-pn)/abs(pn1-p0);
      pn=pn1;
end
pn1

issues in both

• regardless of what value is passed to the function, you set a=5
• error is an important built-in function, use a different variable name
• you have more p variables than necessary (you only need two)

differences between codes:

• tol is not the same
• "while" error is defined incorrectly
• "while" returns a variable that is never defined (p1)

My comment on consistency referred to the fact that your original "while" screenshot wasn't doing anything in particular each loop.