The entries in tspan must strictly increase or decrease. ode45 Issues

Hello all,

I am writing a script for a missile simulation, where a missile flies from a given altitude and strikes the ground. Initial conditions are X0=[x; y; z; xdot; ydot; zdot]. XYZ are coordinates and the dots are the velocities.

I have to make a function for the derivative of X0, which is then integrated by ode45 to make a new X, which is put back through the script over and over until the missile strikes the ground.

function xDot = dxdt(t,X)

xDot = [X(4,1);X(5,1);X(6,1);A(1,1);A(2,1);A(3,1)]
end

For the first iteration of the above function, X is the initial condition X0. xDot is equal to the velocity components in the X, and accelerations denoted by A.

The ode45 function must follow this form.

[time,X]=ode45(@dxdt,[t t+dt],X0);

The time interval for this simulation is only 5 seconds, with increments of 0.01 seconds.

How can I make this function continually iterate, making a new vector X, finding the xDot of that X, then putting it through the ode45, and so on, for possibly 20 iterations?

t=[0 10]
dt = 0.01
tspan= [t t+dt]
[t,X]=ode45(@dxdt,tspan,X0)

This gives the error

Error using odearguments (line 87)

The entries in tspan must strictly increase or decrease.

Error in ode45 (line 115)

odearguments(FcnHandlesUsed, solver_name, ode, tspan, y0, options, varargin);

Error in V2_0 (line 20)

[t,X]=ode45(@xDot,tspan,X0)

Please help.

Answer 1

[madhan ravi]

tspan= t(1):dt:t(end);

Answer 2

[Walter Roberson]

tspan= t + [0, dt];

Note: instead of looping, you should consider using an ode event function to detect when the ground is hit and terminate then.