Bisection method- code stops after one iteration
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Hi, my code doesn't seem to continue beyond the first iteration of the bisection method in my loop. I also am not getting the right answer. I'm not sure where the mistake is.
function c = findroot(f,a,b,e)
% a is the initial value
% b is the final value
% e is the tolerance
if f(a)*f(b)>0
error('f(a) and f(b) must have opposite signs')
end
c = (a+b)/2;
while abs(b-c) <= e;
f = f(c);
break
if f(a)*f(c) <= 0;
c = b;
f(c) = f(b);
else
c = a;
f(c) = f(a);
end
end
end
I am calling the following in the command window:
>> f = @(x) x.^2-x-1;
>> findroot(f, 1, 2, 0.001)
采纳的回答
Torsten
2015-12-4
function c = findroot(f,a,b,e)
% a is the initial value
% b is the final value
% e is the tolerance
left = a;
right = b;
middle = (left+right)/2;
fleft = f(left);
fright = f(right);
fmiddle = f(middle);
if fleft*fright > 0
error('f(a) and f(b) must have opposite signs')
end
while right-left >= e && abs(fmiddle) >= e
if fmiddle*fleft <= 0
right = middle;
fright = fmiddle;
else
left = middle;
fleft = fmiddle;
end
middle = (left+right)/2;
fmiddle = f(middle);
end
c = middle;
end
Best wishes
Torsten.
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