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

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Pooneh Shah Malekpoor 2020-7-9

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https://ww2.mathworks.cn/matlabcentral/answers/562187-the-error-the-function-values-at-the-interval-endpoints-must-differ-in-sign-fzero

评论： Pooneh Shah Malekpoor 2020-7-10

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),