the error"The function values at the interval endpoints must differ in sign" + fzero

Hello. I want to solve the beneath nonlinear eqn(there is only one variable) as the code below. When using fzero, I get the error as"The function values at the interval endpoints must differ in sign.". I know there is a correct root at x=3.47 (which i am looking for).... Is my coding for fzero correct?

c=0
while Error>tol
c=c+1
 syms x positive
for i=1:n+1

    if i==1
        EE(1,1)=0;
    
    else
    EE(i,1)=(((C*l(i-1)*x)+(((tan(phi*pi/180))*x)*((rho*9.81*A(i-1)*(cos(beta(i-1))))+(EE(i-1)*(sin(beta(i-1)-(te))))))-(rho*9.81*A(i-1)*(sin(beta(i-1))))+(EE(i-1)*(cos(beta(i-1)-(te)))))/((cos(beta(i-1)-(te)))+((sin(beta(i-1)-(te)))*(tan(phi*pi/180))*x)));

     end
end

eqn = (simplify((EE(n+1,1))));

fh = @(x) (eqn);% you should use matlabFunction's 'vars' option to convert the variables into a vector.
if c==1
     x0=[0 5];
else 
    x0=k
end
 [x,fval,exitflag] =fzero(fh,x0),

[madhan ravi]

 x0 = 5

[Pooneh Shah Malekpoor]

I replaced the range for x=[0 5] as you mentioned with x0=5 but I get the following error" Exiting fzero: aborting search for an interval containing a sign change because no sign change is detected during search. Function may not have a root.

x =

NaN

fval =

NaN

[madhan ravi]

Or 3?

[Pooneh Shah Malekpoor]

Again, the same error.

As I could get the result from

[k] = vpasolve(eqn, x ,[0 5]);

Dont you think the function handle that i have created is wrong(i.e. fh = @(x) (eqn) )?

Answer 1

[madhan ravi]

 fh = @(x) matlabFunction(eqn)

[Pooneh Shah Malekpoor]

I changed the code as you mentioned:

fh = @(x) matlabFunction(eqn);
if c==1
     x0=5;
else 
    x0=k
end
 [x,fval,exitflag] =fzero([fh],{x0}),

Then I came across this error:"FZERO accepts inputs only of data type double."

[madhan ravi]

{x0} -> x0 why do you complicate things ? XD

[Pooneh Shah Malekpoor]

fh = @(x) matlabFunction(eqn);
if c==1
     x0=5;
else 
    x0=k
end
 [x,fval,exitflag] = fzero(fh,x0);

Ok, then this error!

"Undefined operator '==' for input arguments of type 'function_handle'."

[madhan ravi]

What’s value of c?

[Pooneh Shah Malekpoor]

I prefered to use vpasolve as I got errors each time.

Thanks