Unrecognized function or variable 'FalsePosition'.

13 次查看（过去 30 天）
Fatih Güler
Fatih Güler 2020-12-13
评论： Walter Roberson 2020-12-13
V=40;
rho=1.23;
D=0.005;
mu=1.79E-5;
epsilon=0.0015E-3;
Re=rho*V*D/mu;
f=@(x)(1./sqrt(x)+2*log10(epsilon./(3.7*D)+2.51./(Re*sqrt(x))));
xplot=0.008:0.001:0.08;
plot(xplot,f(xplot))
xlabel("f")
ylabel('y(f)')
grid on
a=0.008;
b=0.08;
tol=0.0001;
disp('iterNo lowerB upperB f(a) f(b) approxRoot f(r) error ')
fstats=FalsePosition(f,a,b,tol);
disp(fstats)
norows=size(fstats,1);
nocols=size(fstats,2);
froot=fstats(norows,nocols-2);
fprintf("Root by false position method =%f\n",froot);
function stats=FalsePosition(f,a,b,tol);
i=1;
iterNo=[i];
lowerB=[a];
upperB=[b];
functValueL=[f(a)];
functValueU=[f(b)];
approxRoot=[];
functValueR=[];
error=[];
if f(a)*f(b)>0
disp('The value of f(a)*f(b)<0,choose other values of a and b')
else
xn=f(b);
xn_1=f(a);
r=b-(xn*(b-a))/(xn-xn_1);
err=abs(f(r));
approxRoot(i)=r;
functValueR(i)=f(r);
error(i)=err;
while err >tol
i=i+1;
iterNo(i)=i;
if xn_1*f(r)<0
b=r;
else
a=r;
end
r=b-(xn*(b-a))/(xn-xn_1);
err=abs(f(r));
upperB(i)=b;
lowerB(i)=a;
functValueU(i)=f(b);
functValueL(i)=f(a);
approxRoot(i)=r;
functValueR(i)=f(r);
error(i)=err;
end
end
stats=[iterNo;lowerB;upperB;functValueL;functValueU;approxRoot;functValueR]
end

请先登录，再回答此问题。

采纳的回答

Alan Stevens
Alan Stevens 2020-12-13
It works just fine for me! (I copied it into a script, saved the script and then clicked the Run arrow).
  1 个评论
Walter Roberson
Walter Roberson 2020-12-13
Ran in:
The plot shows a zero near 0.03 but the reported false position is near -0.001 . This is because the error compared to the root (last row) is being displayed instead of the position of the root (second last row)
V=40;
rho=1.23;
D=0.005;
mu=1.79E-5;
epsilon=0.0015E-3;
Re=rho*V*D/mu;
f=@(x)(1./sqrt(x)+2*log10(epsilon./(3.7*D)+2.51./(Re*sqrt(x))));
xplot=0.008:0.001:0.08;
plot(xplot,f(xplot))
xlabel("f")
ylabel('y(f)')
grid on
a=0.008;
b=0.08;
tol=0.0001;
disp('iterNo lowerB upperB f(a) f(b) approxRoot f(r) error ')
iterNo lowerB upperB f(a) f(b) approxRoot f(r) error
fstats=FalsePosition(f,a,b,tol);
disp(fstats)
1.0000 2.0000 3.0000 4.0000 5.0000 6.0000 7.0000 8.0000 9.0000 10.0000 11.0000 12.0000 13.0000 14.0000 15.0000 0.0080 0.0080 0.0080 0.0080 0.0234 0.0284 0.0284 0.0284 0.0284 0.0288 0.0288 0.0290 0.0290 0.0290 0.0290 0.0800 0.0570 0.0413 0.0307 0.0307 0.0307 0.0299 0.0294 0.0291 0.0291 0.0290 0.0290 0.0290 0.0290 0.0290 5.8343 5.8343 5.8343 5.8343 0.7447 0.0720 0.0720 0.0720 0.0720 0.0137 0.0137 0.0012 0.0012 0.0012 0.0012 -2.7416 -1.9559 -1.0987 -0.1884 -0.1884 -0.1884 -0.1083 -0.0522 -0.0132 -0.0132 -0.0046 -0.0046 -0.0028 -0.0015 -0.0006 0.0570 0.0413 0.0307 0.0234 0.0284 0.0299 0.0294 0.0291 0.0288 0.0290 0.0290 0.0290 0.0290 0.0290 0.0290 -1.9559 -1.0987 -0.1884 0.7447 0.0720 -0.1083 -0.0522 -0.0132 0.0137 -0.0046 0.0012 -0.0028 -0.0015 -0.0006 -0.0000
norows=size(fstats,1);
nocols=size(fstats,2);
froot=fstats(norows,nocols-2);
fprintf("Root by false position method =%f\n",froot);
Root by false position method =-0.001498
function stats=FalsePosition(f,a,b,tol);
i=1;
iterNo=[i];
lowerB=[a];
upperB=[b];
functValueL=[f(a)];
functValueU=[f(b)];
approxRoot=[];
functValueR=[];
error=[];
if f(a)*f(b)>0
disp('The value of f(a)*f(b)<0,choose other values of a and b')
else
xn=f(b);
xn_1=f(a);
r=b-(xn*(b-a))/(xn-xn_1);
err=abs(f(r));
approxRoot(i)=r;
functValueR(i)=f(r);
error(i)=err;
while err >tol
i=i+1;
iterNo(i)=i;
if xn_1*f(r)<0
b=r;
else
a=r;
end
r=b-(xn*(b-a))/(xn-xn_1);
err=abs(f(r));
upperB(i)=b;
lowerB(i)=a;
functValueU(i)=f(b);
functValueL(i)=f(a);
approxRoot(i)=r;
functValueR(i)=f(r);
error(i)=err;
end
end
stats=[iterNo;lowerB;upperB;functValueL;functValueU;approxRoot;functValueR];
end

请先登录，再进行评论。

更多回答（0 个）

类别

在 Help Center 和 File Exchange 中查找有关 Electrical Block Libraries 的更多信息

标签

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by