vehicle dynamics code problems

says t isn't defined and gives me a hard time. Where t is the time component of the function.

%%VEHICLE_MODEL IDNLGREY model file

%%function [dx,y] = VEHICLE_MODEL(t, x, u, m, a, b, Cy, varargin)

function [dx,y] = VEHICLE_MODEL_test(t, x, u, m, a, b, Cy, varargin)

%% prompt = 'Please enter the intial start time. ';

%% t = input(prompt);

%% prompt = 'Please enter the Vehicle Mass in Kg ';

%% m = input(prompt);

% function parameters:

% t: the current time

% x: the state vector at time t

% u: the input vector at time t

% m: mass of the vehicle [kg]

% a: distance from front axle to COG [m]

% b: distance from rear axle to COG [m]

% Cy: lateral tire stiffness (Axis skew stiffness) [N/rad]

% varargin: optional inputs to the model file

J = m * 0.25 *(a+b)^2; % moment of inertia [kg*m^2]

Fyf = Cy*(u(1)-atan((x(4)+a*x(2))./x(3))); % lateral tire force on front tires [N]

Fyr = -Cy*atan((x(4)-b*x(2))./x(3)); % lateral tire force on rear tires [N]

vx_inertial = x(3).*cos(x(1))-x(4).*sin(x(1)); % longitudinal velocity in inertial reference frame [m/s]

vy_inertial = x(3).*sin(x(1))+x(4).*cos(x(1)); % lateral velocity in inertial reference frame [m/s]

% state equations.

dx = [x(2); ... % yaw angle velocity [rad/s]

1/J*(a*(u(2)*sin(u(1))+Fyf*cos(u(1)))-b*Fyr); ... % yaw angle accel. [rad/s^2]

1/m*(u(2)*cos(u(1))-Fyf*sin(u(1))+u(3))+x(4).*x(2); ... % longitudinal accel. in body reference frame [m/s^2]

1/m*(u(2)*sin(u(1))+Fyf*cos(u(1))+Fyr)-x(3).*x(2); ... % lateral accel. in body reference frame [m/s^2]

vx_inertial; ... % longitudinal velocity in inertial reference frame [m/s]

vy_inertial ... % lateral velocity in inertial reference frame [m/s]

];

% output equations.

y = [x(1); ... % yaw angle [rad]

x(2); ... % yaw angle velocity [rad/s]

x(3); ... % longitudinal velocity in body reference frame [m/s]

x(4); ... % lateral velocity in body reference frame [m/s]

x(5); ... % longitudinal position in inertial reference frame [m]

x(6); ... % lateral position in inertial reference frame [m]

vx_inertial; ... % longitudinal velocity in inertial reference frame [m/s]

vy_inertial; ... % lateral velocity in inertial reference frame [m/s]

Fyf; ... % lateral tire force on front tires [N]

Fyr ... % lateral tire force on rear tires [N]

];

end