# Numerical method to solve high order ODEs.

1. Aug 27, 2008

### meridian

here is a simplified version of my working equtions
$$y''' = \frac{(y'' y+y' y) y + y'y''}{y' + y''}$$
and 3 related boundary conditions, is there some hints to solve such equation numerically?

ThX

2. Aug 27, 2008

### Defennder

This might sound crazy, but note that everything here is a function of y. You may not have to resort to numerical solutions. But then again I haven't tried it out yet. Looks a little intimidating.

3. Aug 27, 2008

### meridian

in the equation,
$$y = y(x)$$
The original equation are much more complex, it is not possible to get a exact analytical solution for that. What I want to learn is the general numerical method to solve such equation.

4. Aug 27, 2008

### HallsofIvy

Staff Emeritus
Let u= y'(x), v= y"(x). Then your equation is becomes
$$y'= \frac{(v y+u y) y + uv}{y + v}$$
That together with y'= u and u'= v gives you three interconnected first order equations. Do, say, a 4th order Runge-Kutta, advancing the step in all three equations at the same time.

5. Aug 27, 2008

### Topher925

Thats would I would suggest. Although the Adams-Moulton-Bashforth method would work as well and probably give you a little bit more accuracy. But you will need the RK4 for the first couple steps anyway.