Second order pde - on invariant?

[sigh1342]

second order pde -- on invariant?

What the meaning for a second order pde is rotation invariant?
Is all second order pde are rotation invariant? or only laplacian?

 

[Simon Bridge]

Well, do you know what "rotation invarient" means to start with?
It sounds like you've come across the terms as part of a course involving laplacians - in which case, you were shown a proof somewhere that the laplacian is rotation invarient. What was the condition the laplacian had to satisfy for the proof to work? Do all 2ndO PDEs satisfy this condition?