Fzero function errors in matlab

xN = zeros(1,Niter); % dispalcemant analytical
dxN = zeros(1,Niter); % dispalcemant_dot analytical
ddxN = zeros(1,Niter); % dispalcemant_double_dot analytical

xN(1) = x0; % initial displacement
xN(2) = x0 + v0*dt; % displacement at iteration 2

dxN(1) = v0; %initial vel
dxN(2) = v0; 

Const_drag = 0.5*Cd*p*A;
Const_lift = 0.5*Cl*p*A;

for i = 3:Niter

    xNOW = xN(i-1);
    xPRE = xN(i-2);

    f = @(xNEX) ...
        m * (xNEX - 2*xNOW + xPRE)/(dt^2)...
        + 0.5 * Const_drag * ((xNEX-xPRE)/(2 * dt))...
        + (-0.0001 * (w + Const_lift * ((xNEX-xPRE)/(2 * dt))^2)^2)...
        + 1.6 * (w + Const_lift * ((xNEX-xPRE)/(2 * dt)) ^ 2);
    xNEX = fzero(f, xNOW);
    xN(i) = xNEX;
    dxN(i) = (xNEX - xPRE)/(2*dt);
  
end


% xNEX = fzero(f, xNOW); this line keep showing errors but i could not figure out 

[Shravan Kumar Vankaramoni]

Can you provide the error message thrown on that line?