Using fzero to solve an equation with different constants every time

Hello, I want to solve for x(i) the function F for multiple values of theta and record each x(i). I used the code below to do it but the following error appears:

Error using fzero (line 290)

The function values at the interval endpoints must differ in sign.

Error in main (line 20)

xsol(i)=fzero(@obj_fun,x0);

I do not know why this happens.Any help would be greatly appreciated!

function xsol=main() 
r=0.03172;
s=0.333;
rho=0.01;
b=2.5;
tau=0.286;
x0=[0;1];

%values for tau
theta_pool = 0:0.01:0.75;

%Call fsolve in a loop
for i = 1 : numel(theta_pool)
    theta = theta_pool(i);
    xsol(i)=fzero(@obj_fun,x0);
end

function F = obj_fun(x)
F=(r*((1-tau)*s*(x.^(1-s))*(1-theta))/(r-theta*(1-tau)*s*x.^(1-s)))- rho -(x.^(s)/b)-r+(tau/b);
end
end
%call the result by typing result=main 

Answer 1

[Jeremy]

x0=[0;1];

By passing a vector into fzero you are telling it that you think the solution is between these values, so it will start using this interval. I ran your code replacing this with x0 = 0; and it would appear that the solution to your equation is complex on every iteration. So, fzero only returns a bunch of NaN results

[Catherine Castiblanco]

I see, but I still have 2 questions

1. Why it only shows 76 results
2. And, is there another function I can use so matlab show me the complex numbers?

Thank you!

[Jeremy]

You need to provide a better initial guess (or range) for fzero to iterate on. For example, I changed x0 to 10, and I get real numbers for the first 14 results, and then back to NaN for the remaining. I plotted the case where theta = 0 to get a better idea of where the function is real and close to zero