Why this code doesn't work?

I am trying to get a velocity plot but the code doesn't work and I can't fix it.

ti=0.0; tf=15.0; ui=30.0;
m=2585; g=10; W=m*g; Theta=0.0; Fx=-2000;
f=0.03; rho=1.225; Cd=0.2; A=2.9; uw=0.0;
tol=1.0E-4; trace=1;
[t,u]= ode23("asdfg",ti,tf,ui,tol,trace);
plot(t,u,"r")
title("Vehicle Forward Speed");
xlabel("Time(sec)")
ylabel("u(m/sec)"); grid;
function udot = asdfg(t,u) 
if u>0
    udot=(1/m)*(Fx-W*sin(Theta)-f*W*cos(Theta)-0.5*rho*Cd*A*(u+uw)^2);
else
    udot=0;
end
end

This was the last code I tried and I got this error message:

Error using odearguments

The last entry in tspan must be different from the first entry.

Error in ode23 (line 106)

odearguments(odeIsFuncHandle, odeTreatAsMFile, solver_name, ode, tspan, y0, options, varargin);

Error in untitled (line 5)

[t,u]= ode23("asdfg",ti,tf,ui,tol,trace);

Answer 1

[Torsten]

ti=0.0; tf=15.0; ui=30.0;
m=2585; g=10; W=m*g; Theta=0.0; Fx=-2000;
f=0.03; rho=1.225; Cd=0.2; A=2.9; uw=0.0;
tol=1.0E-4; trace=1;
options = odeset('RelTol',tol,'AbsTol',tol);
[t,u]= ode23(@(t,u)asdfg(t,u,m,Fx,W,Theta,f,rho,Cd,A,uw),[ti,tf],ui,options);
plot(t,u,"r")
title("Vehicle Forward Speed");
xlabel("Time(sec)")
ylabel("u(m/sec)"); grid;

function udot = asdfg(t,u,m,Fx,W,Theta,f,rho,Cd,A,uw)
if u>0
    udot=(1/m)*(Fx-W*sin(Theta)-f*W*cos(Theta)-0.5*rho*Cd*A*(u+uw)^2);
else
    udot=0;
end
end