bisection method error symbolic

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hi i'm trying to write a code to solve this question:
the code below need some adjustment to make it work
clear
clc
syms y
q=20;
g=9.8;
b=3+y;
ac=3*y+((y^2)/2);
f=@(y) 1-((q^2)/(g*ac^3)*b);
x1=0.5
x1 = 0.5000
xu=2
xu = 2
ezplot(f(y))
grid on
hold on
for i=1:100
xr(i)=(x1+xu)/2
if ((f(x1)*f(xr(i)))<0)
xu=xr(i)
elseif ((f(x1)*f(xr(i))>0))
x1=xr(i)
elseif ((f(x1)*f(xr(i))==0))
break
end
if ((i>1)&&(abs((xr(i)-xr(i-1)))/xr(i-1))*100<0.01)
break
end
plot(xr(i),f(xr(i)),'xr')
end
xr = 1.2500
Conversion to logical from sym is not possible.
xr(10)

Accepted Answer

Torsten
Torsten on 7 Oct 2022
syms y
q=20;
g=9.8;
b=3+y;
ac=3*y+y^2/2;
f= 1-q^2/(g*ac^3)*b;
x1=0.5;
xu=2.5;
hold on
fplot(f,[0.5 2.5])
grid on
f = matlabFunction(f);
for i=1:100
xr(i)=(x1+xu)/2;
if ((f(x1)*f(xr(i)))<0)
xu=xr(i);
elseif ((f(x1)*f(xr(i))>0))
x1=xr(i);
elseif ((f(x1)*f(xr(i))==0))
break
end
if ((i>1)&&(abs((xr(i)-xr(i-1)))/xr(i-1))*100<0.01);
break
end
end
plot(xr,f(xr),'xr')
hold off
  1 Comment
Faisal Al-Wazir
Faisal Al-Wazir on 7 Oct 2022
nice but i did it in another way
clear
clc
q=20;
g=9.8;
syms w
f=@(w) 1-((q^2)/(g*(3*w+((w^2)/2))^3)*(3+w));
f=@(y) 1-((q^2)/(g*(3*y+((y^2)/2))^3)*(3+y));
x1=0.5
x1 = 0.5000
xu=2
xu = 2
ezplot(f(w))
grid on
hold on
for i=1:10
xr(i)=(x1+xu)/2
if ((f(x1)*f(xr(i)))<0)
xu=xr(i)
elseif ((f(x1)*f(xr(i))>0))
x1=xr(i)
elseif ((f(x1)*f(xr(i))==0))
break
end
if ((i>1)&&(abs((xr(i)-xr(i-1)))/xr(i-1))*100<0.01)
break
end
plot(xr(i),f(xr(i)),'or')
end
xr = 1.2500
x1 = 1.2500
xr = 1×2
1.2500 1.6250
xu = 1.6250
xr = 1×3
1.2500 1.6250 1.4375
x1 = 1.4375
xr = 1×4
1.2500 1.6250 1.4375 1.5312
xu = 1.5313
xr = 1×5
1.2500 1.6250 1.4375 1.5312 1.4844
x1 = 1.4844
xr = 1×6
1.2500 1.6250 1.4375 1.5312 1.4844 1.5078
x1 = 1.5078
xr = 1×7
1.2500 1.6250 1.4375 1.5312 1.4844 1.5078 1.5195
xu = 1.5195
xr = 1×8
1.2500 1.6250 1.4375 1.5312 1.4844 1.5078 1.5195 1.5137
x1 = 1.5137
xr = 1×9
1.2500 1.6250 1.4375 1.5312 1.4844 1.5078 1.5195 1.5137 1.5166
xu = 1.5166
xr = 1×10
1.2500 1.6250 1.4375 1.5312 1.4844 1.5078 1.5195 1.5137 1.5166 1.5151
xu = 1.5151
xr(10)
ans = 1.5151

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