# Matlab ode45 Problem

1. Mar 2, 2013

### eurekameh

I'm trying to solve an ODE using matlab's ode45, but I'm receiving the following error:

Warning: Failure at t=4.509803e+01. Unable to meet integration tolerances without reducing the step size below the smallest value allowed (1.136868e-13) at time t.

Can anybody explain what this means?

2. Mar 2, 2013

### SteamKing

Staff Emeritus
Sounds like ode45 is having trouble converging on a solution.

In order to diagnose the problem in more detail, you should probably post the ODE you are trying to solve.

3. Mar 3, 2013

### eurekameh

function dxdt = test(t,x)
mu = 398600.64;
dxdt_1 = x(2);
dxdt_2 = (-mu/x(1)^3)*x(1);
dxdt = [dxdt_1;dxdt_2];

It's a second-order ODE and I'm trying to solve it from the time interval of 0 to 28800. When I lower this time interval to something like 50, the program seems to work fine, but anything higher than that, it stops to converge. Here is my code to run it:

t = 0:28800
[t x] = ode45(@test,t,[1000;-7]);

4. Mar 3, 2013

### SteamKing

Staff Emeritus
I don't have the ODE you are trying to solve, only your reformulation for Matlab.

5. Mar 3, 2013

### eurekameh

I'm trying to solve the orbit motion of equation x,doubledot = (-mu/x^3)*x, with an initial condition of x0 = 1000, and xdot,0 = -7.

6. Mar 4, 2013

### eurekameh

Do you know why it's not converging?