Not able to find fzero

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Dhawal Beohar 2022-5-25

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1727020-not-able-to-find-fzero

评论： Dhawal Beohar 2022-8-7

--> difference.m
function y = difference(u,d1,n,a,m,T,PsByN_0,UmaxN_0)
d1=20;
n=10^-11.4;
m=2.7;
a=0.5;
T=1;
PsByN_0dB=5;                                                     
PsByN_0=10.^(PsByN_0dB/10);
UmaxdB = 5;
UmaxN_0=10.^(UmaxdB/10);
fun1 = (-1./u)*log(((d1^m)./(a*n*PsByN_0*T*u+d1^m)*a)./(1-a));
fun2 = (1./u)*log(((-exp(u*UmaxN_0)*(exp(-PsByN_0*u)))./(u*UmaxN_0+PsByN_0*u))*(PsByN_0*u)-(PsByN_0*u*(exp(-PsByN_0*u)))*(expint(u*UmaxN_0+PsByN_0*u))+(exp(-PsByN_0*u))+((PsByN_0*u)*(exp(-PsByN_0*u)))*(expint(PsByN_0*u))+(exp(u*UmaxN_0))./((UmaxN_0/PsByN_0)+1));
y = (fun1 - fun2);
g0=fzero(@(u) difference(u,d1,n,a,m,T,PsByN_0,UmaxN_0), 10);
end
        

采纳的回答

Torsten 2022-5-25

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1727020-not-able-to-find-fzero#answer_971600

在 MATLAB Online 中打开

d1=20;
n=10^-11.4;
m=2.7;
a=0.5;
T=1;
PsByN_0dB=5;                                                     
PsByN_0=10.^(PsByN_0dB/10);
UmaxdB = 5;
UmaxN_0=10.^(UmaxdB/10);
fun1 = @(u) (-1./u)*log(((d1^m)./(a*n*PsByN_0*T*u+d1^m)*a)./(1-a));
fun2 = @(u) (1./u)*log(((-exp(u*UmaxN_0)*(exp(-PsByN_0*u)))./(u*UmaxN_0+PsByN_0*u))*(PsByN_0*u)-(PsByN_0*u*(exp(-PsByN_0*u)))*(expint(u*UmaxN_0+PsByN_0*u))+(exp(-PsByN_0*u))+((PsByN_0*u)*(exp(-PsByN_0*u)))*(expint(PsByN_0*u))+(exp(u*UmaxN_0))./((UmaxN_0/PsByN_0)+1));
fun =@(u) (fun1(u) - fun2(u));
g0=fzero(fun, 10);

21 个评论
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Torsten 2022-8-6

在 MATLAB Online 中打开

I suggest you try an interval around the zero you found, e.g.

u = fzero(fun,[0.01,0.02])
U = linspace(0.01,0.02,20);
fU = fun(U);
plot(U,fU)

Dhawal Beohar 2022-8-6

ok, thanks!

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更多回答（1 个）

Sam Chak 2022-5-25

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1727020-not-able-to-find-fzero#answer_971595

在 MATLAB Online 中打开

Hi @Dhawal Beohar

Guess the problem that you want to solve is a complex-valued function.

function y = difference(u)

% parameters

d1 = 20;

n = 10^-11.4;

m = 2.7;

a = 0.5;

T = 1;

PsByN_0dB = 5;

PsByN_0 = 10.^(PsByN_0dB/10);

UmaxdB = 5;

UmaxN_0 = 10.^(UmaxdB/10);

% functions

fun1 = (-1./u)*log(((d1^m)./(a*n*PsByN_0*T*u + d1^m)*a)./(1 - a));

fun2 = (1./u)*log(((- exp(u*UmaxN_0)*(exp(-PsByN_0*u)))./(u*UmaxN_0 + PsByN_0*u))*(PsByN_0*u) - (PsByN_0*u*(exp(-PsByN_0*u)))*(expint(u*UmaxN_0 + PsByN_0*u)) + (exp(-PsByN_0*u)) + ((PsByN_0*u)*(exp(-PsByN_0*u)))*(expint(PsByN_0*u)) + (exp(u*UmaxN_0))./((UmaxN_0/PsByN_0) + 1));

y = (fun1 - fun2);

end

Let's try with fzero first.

[u, fval, exitflag, output] = fzero(@(u) difference(u), 10)

The exitflag = -4 indicates that complex function value was encountered while searching for an interval containing a sign change.

Next, fsolve is used.

[u, fval, exitflag, output] = fsolve(@(u) difference(u), 10)

The exitflag = -2 means that the Equation is not solved. The exit message shows that fsolve stopped because the problem appears regular as measured by the gradient, but the vector of function values is not near zero as measured by the default value of the function tolerance.