Struggling to use fzero on this function

I am trying to solve for when y=0 with u as the variable for the function below.

When I try v= fzero(@(u) velocity(u,-1,250E-6, 0.13))

MATLAB says:

FZERO requires at least two input arguments or a structure with valid fields.

Any ideas?

function y=velocity(u,z,Ro,H)

p_sat = 2.3393E3; Patm = 100E3; rho_f = 998.21; g = 9.81; Pl = Patm-rho_f*g*z; gamma = 7.28E-2;

p =[Pl-p_sat 2*gamma 0 -(Patm+rho_f*g*H)*Ro^3]; R = roots(p); % get all roots of p R = R(imag®==0); % only keep real roots

Vb=(4.*pi.*R^3)./3;

g = 9.81; rho_f = 998.21; temp = 20+273; R_g = 8.3145; y_air = 1-((p_sat)./(Pl.*((Ro./R).^3))); y_water = 1-y_air; Mr = (28.9647./1000).*y_air + (18./1000)*y_water; Pb = Pl+((2.*gamma)/R); rho_b = (Pb./(R_g.*temp)).*Mr; mu = 0.0010005; d = 2.*R;

Re =((rho_f*u*d)/mu) cd =(24/Re)*(1+0.15*Re.^0.687)

y=Vb.*g.*(rho_f-rho_b)-cd.*((pi.*d.^2)/4)*((rho_f*u.^2)/2)

end

Answer 1

[Steven Lord]

You need to tell fzero either a starting point or an interval in which you know a zero exists. This means fzero needs to be called with at least two inputs (the second of which is a scalar or a 2-element vector) or if you call it with one input that input needs to be a problem structure that contains that information.

[Jan]

+1. Exactly.

@ZM: The error message is clear already

 FZERO requires at least two input arguments or a structure
 with valid fields.

If you get such a message, start with reading the documentation:

help fzero

You will find the code example X = fzero(FUN,X0) in the first line and this is the solution already: X0 is missing.

Answer 2

[ZM]

Ah ok, rookie error. Thanks!

Answer 3

[Toluwaloju Tunde Isaiah]

I am trying to solve the following using the fzero command

L=0.035:-0.001:0

for k=1;

while k<=length(L);

L=L(:,k);

fun_=@(x)det([(cosh(x)+cos(x))-(x.^3)*(In/(M*L.^2))*(sinh(x)+sin(x))-(x.^2)*(Ms/(M*L))*(cosh(x)-cos(x)) (sinh(x)+sin(x))-

(x.^3)*(In/(M*L.^2))*(cosh(x)-cos(x))-(x.^2)*(Ms/(M*L))*(sinh(x)-sin(x)); (sinh(x)-sin(x))+(x)*(m0/M)*(cosh(x)-cos(x))+(x.^2)*

(Ms/(M*L))*(sinh(x)+sin(x)) (cosh(x)+cos(x))+(x)*(m0/M)*(sinh(x)-sin(x))+(x.^2)*(Ms/(M*L))*(cosh(x)-cos(x))]);

fun(k)=fzero(@(x)fun_(x));

fun(k)=fzero(@(x)fun_(x,L));

its = [fzero(fun(k),0.1) fzero(fun(k),0.3) fzero(fun(k),0.5) fzero(fun(k),0.7)];

itss = its(its>0);

betaN = min(itss)

wn=(betaN(k)^2)*sqrt(E*I_s/(Rho*A*(L^4)));

fn=wn/(2*pi)

fprintf('Mode shape # %2f corresponds to nat. freq (wn): %f\n', k, wn(k) );

k=k+1;

end

end

M, L, m0, In, Ms, are known scalers

The Line of error feed back i recieved follows

Error using fzero (line 116)

FZERO requires at least two input arguments or a structure with valid fields.

Error in PiezowithTunability (line 55)

fun(k)=fzero(@(x)fun_(x,L));