# 17. Using SciPy’s ODEINT solver

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HI, I’m Massimiliano.
My best compliments for your Courses. I find them great!

In this lesson, I have a problem with ODEINT. My problem is to understand how ODEINT manages the functions and give the solutions in the correct position in the list solution. Looking at the function passed in ODEINT through SystemEquation, how does ODEINT relate U1 to Y1, and so further? Otherwise, U1, U2, and U3 seem to be treated as constants. But the solution is made of 6 values.

I’m missing the point here. Thank you for any hint.
Thank you,
Massimiliano

Hi Massimiliano,

I’m not sure I fully understand your question. Please feel free to elaborate.

To recap, the `systemEquations` function simply returns the equations, recast as 6 first order ODEs rather than 3 second order ODEs. The position and velocity state variables are…

``````u1 = mass 1 position
y1 = mass 1 velocity
u2 = mass 2 position
y2 = mass 2 velocity
u3 = mass 3 position
y3 = mass 3 velocity
``````

With these defined, we can write (and return) the system equations (as first order ODEs).