I am trying to plot a figure with different value of a parameter but the graph is plotting on negative Y axis.

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Dhawal Beohar
Dhawal Beohar 2022-7-25
编辑： dpb 2022-7-29
I am trying to plot a figure with different value of 'a' but when I am entering value of 'a' below 0.5, the graph is plotting on negative axis. As the equation I am plotting is effective capapcity equation, it can't be negative. Same is happening when I am plotting 'fun'.
I have attached the figure for reference.
function y = difference(u,d1,n,a,m,T,PsByN_0,UmaxN_0)
d1=20;
n=10^-11.4;
ne=0.5;
m=2.7;
a=0.40;
T=1;
PsByN_0dB=15;
PsByN_0=10.^(PsByN_0dB/10);
UmaxdB = 15;
UmaxN_0=10.^(UmaxdB/10);
%u = 0.01678
u=0.001:0.001:0.5;
fun1 = @(u) (1./u).*log(((d1^m)./(a.*ne.*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,[0.001, 0.02])
g0 = fzero(fun,[0.01])
fun1(g0)
fun2(g0)
plot(u,fun1(u));
hold on;
grid on;
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dpb
dpb 2022-7-29
编辑：dpb 2022-7-29
"Both might be incorrect, but at least fun2 is incorrect."
It's also possible both are correct but the hypothesis they intersect is wrong -- or one or more of the other constants is/are wrong to shift the solution for fnA() above to be >0 such that fun1() is also positive.
Or, they could be the correct solution to the wrong problem; or there are incorrect assumptions (or at least unfulfilled/inconsistent with) in the formulation of the problem itself.
We've no knowledge of the problem; no way to judge the applicability of the solution/methods and even if work through the math, certainly no idea of particular constants.

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