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Bisection Method Code Help

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Angelina Encinias
Angelina Encinias 2022-8-31
编辑： Torsten 2022-8-31
Help with my code. Only spits out one value.
Function File:
%Script File:
func=@(x) sin(10*x)+cos(3*x);
xl=3; xu=5;
x=bisection1(func,xl,xu)
function root=bisection1(func,x1,xu)
xr=x1;es=.0001;
i=0;
while i<6
i=i+1;
xrold=xr;
xr=(x1+xu)/2;
if xr~=0
ea=abs((xr-xrold)/xr)*100;
root=xr
else
ea=100;
root=xr
end
if func(x1)*func(xr)<0
xu=xr;
root=xr
elseif func(x1)*func(xr)>0
x1=xr;
root=xr
else
ea=0;
root=xr
end
if ea<=es,break,end
end
root=xr;
end

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回答（1 个）

Torsten
Torsten 2022-8-31
Ran in:
I didn't check whether there is a programming error in bisection1. In comparison to fzero it's very inexact - that's for sure.
format long
func=@(x) sin(10*x)+cos(3*x);
xl=3.2; xu=3.3;
x(1)=bisection1(func,xl,xu);
x1(1)=fzero(func,[xl,xu]);
xl=3.3; xu=3.4;
x(2)=bisection1(func,xl,xu);
x1(2)=fzero(func,[xl,xu]);
xl=3.6; xu=3.8;
x(3)=bisection1(func,xl,xu);
x1(3)=fzero(func,[xl,xu]);
xl=4.15; xu=4.25;
x(4)=bisection1(func,xl,xu);
x1(4)=fzero(func,[xl,xu]);
xl=4.25; xu=4.35;
x(5)=bisection1(func,xl,xu);
x1(5)=fzero(func,[xl,xu]);
xl=4.5; xu=5;
x(6)=bisection1(func,xl,xu);
x1(6)=fzero(func,[xl,xu]);
x
x = 1×6
3.260937500000000 3.367187500000000 3.746875000000000 4.229687499999999 4.264062500000000 4.710937500000000
x1
x1 = 1×6
3.262423140266324 3.365992128846206 3.745745086972446 4.229067033678568 4.263590029871862 4.712388980384690
func(x)
ans = 1×6
-0.006942296312261 -0.005267769874115 0.014275699455641 -0.000954862685705 0.000745839854238 0.018868721583465
func(x1)
ans = 1×6
1.0e-14 * -0.122124532708767 0.166533453693773 0.333066907387547 -0.044408920985006 0.055511151231258 0.594077493713784
X=3:0.001:5;
plot(X,func(X))
hold on
plot(x,func(x),'o')
function root=bisection1(func,x1,xu)
xr=x1;es=.0001;
i=0;
while i<6
i=i+1;
xrold=xr;
xr=(x1+xu)/2;
if xr~=0
ea=abs((xr-xrold)/xr)*100;
root=xr;
else
ea=100;
root=xr;
end
if func(x1)*func(xr)<0
xu=xr;
root=xr;
elseif func(x1)*func(xr)>0
x1=xr;
root=xr;
else
ea=0;
root=xr;
end
if ea<=es,break,end
end
root=xr;
end

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