MATLAB Answers


Writing function based on a vector of roots

Asked by John
on 28 Feb 2018
Latest activity Commented on by Star Strider
on 1 Mar 2018
In the following code, one of lines plotted is a vector of solutions to a nonlinear function (plotted against a parameter). I want to find the intersection point, but I don't know how to do it. Does anyone have any suggestion?
close all;
clear all;
lambda = 1;
Fprime = @(z) lambda.*exp(-lambda.*z);
F = @(z) 1-lambda.*exp(-lambda.*z);
F2prime = @(z) -lambda^2.*exp(-lambda.*z);
intz = @(z) (1-(lambda.*z+1).*exp(-lambda.*z))./lambda;
funz = @(z) z.*(1-F(z))+intz(z);
ph = 0.8;
pl = 0.4;
t = 0.6;
theta =1.3;
sigma = 0.6;
epsilon = 0.1;
y = @(z,psi) (((ph-pl)/(1-t))*psi*(z.*(1-F(z))+intz(z))).^(1/theta);
u = @(z,psi) ph.*((1+epsilon).*y(z,psi)).^alpha + (1-ph).*y(z,psi).^alpha;
N2 = 200;
psigrid = linspace(.5,5,N2);
zbar2 = zeros(1,N2);
Gfun = @(z,psi) psi.*z;
rhs = @(z,psi) (sigma/.8).*(u(z,psi)-Gfun(z,psi)+(1-ph).*psi.*(1-F(z)).*z);
for k=1:N2
rhstest = @(z) rhs(z,psigrid(1,k));
Gfuntest = @(z) Gfun(z,psigrid(1,k));
zbarfun = @(z) rhstest(z) - Gfuntest(z);
zbar2(1,k) = fsolve(zbarfun,.2);
hold on;


I notified the person at MathWorks who is responsible for ‘Answers’ that your post is not appearing on the main Answers page, for me either. I expect to hear back, so I’ll post back the reason when I hear about it.
It should appear, since Answers spanning about 4 hours are currently posted, and since yours is only 3 hours old, and since my Answer and this Comment are only minutes old, it should be visible.
The Answer I posted should be what you want. Your post is visible on my personal Answers page, so I can follow up on it.
Strangely enough, it's still not showing...
Thank you very much for your help!
As always, my pleasure!
I’ve not heard back yet from Rena Berman. I’ll let you know. She might post back here as well, since I included the URL to your Question in my email to her.

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1 Answer

Answer by Star Strider
on 1 Mar 2018
 Accepted Answer

This will calculate the x-coordinate of the intersection, and plot a green pentagram there:
intx = interp1(zbar2, psigrid, 0.3, 'linear');
hold on;
plot(intx, 0.3, 'pg', 'MarkerFaceColor','g', 'MarkerSize',10)
hold off
The rest of your code (before and including the for loop) is unchanged, so I didn’t post it.


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