Differences between Two Notations in DE

[lkh1986]

Homework Statement

Is there any difference between the two notations below? Or can they be used interchangeably?

\tilde{x} and \underline{x} (not an underline, but the tilde is at the bottom of the unknown x)

Homework Equations

The Attempt at a Solution

From my observation, \underline{x} is mostly used to denote a row matrix, or a vector, while \tilde{x} is used to denote a vector function, is it correct? Thanks.

 

[HallsofIvy]

Those are NOT standard notations so can be used any way you want as long as you define them when you do.