Not sure why the loop's not working??

Question

Nav 2013-5-13

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/75569-not-sure-why-the-loop-s-not-working

the loop parts suppose to repeat until (abs((a+b)^2/(4*t)-pi)<= thres).

a=1;
b=1/sqrt(2);
t=1/4;
x=1;
thres = 0.001;
while abs((a+b)^2/( 4*t )-pi) > thres  
 y=a;
 a=(a+b)/2;
 b=sqrt(b)*sqrt(y);
 t=t-(x)*(y-a)^2;
 x=2*x;
 if (abs((a+b)^2/(4*t)-pi)<= thres)
     break
     mypi= (a+b)^2/(4*t);       
 end
end

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Image Analyst 2013-5-13

Matthew - please change this to an answer, rather than a comment.

Matthew Doveton 2013-5-13

Thanks. Its my first time :)

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Answer 1

Matthew Doveton 2013-5-13

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mypi is never reached due to the positioning of the break statement, should be:

a=1; b=1/sqrt(2); t=1/4; x=1; thres = 0.001; 
while abs((a+b)^2/( 4*t )-pi) > thres 
    y=a; 
    a=(a+b)/2; b=sqrt(b)*sqrt(y); 
    t=t-(x)*(y-a)^2; x=2*x; 
    if (abs((a+b)^2/(4*t)-pi)<= thres) 
        mypi = (a+b)^2/(4*t);
        break 
    end
end