# Decoupled or coupled?

1. Dec 3, 2009

### delve

$$\ddot{x}=\dot{z}$$

$$\ddot{z}=\dot{x}$$

there should be z with a dot above it just like the x, but there is none, and the code is correct as far as I know. Can someone help? Thanks.

Last edited: Dec 3, 2009
2. Dec 3, 2009

### hamster143

Coupled.

Last edited: Dec 3, 2009
3. Dec 4, 2009

### delve

do you know what makes it coupled?

4. Dec 4, 2009

### hamster143

The fact that there are no equations that contain only x or only z.

5. Dec 5, 2009

Thank you :)

6. Dec 5, 2009

### hamster143

Also notice that if you use a substitution u=x+z, v=x-z, you get a pair of uncoupled equations.