When can one Change order of derivatives?

[Charanjit]

Here is an example...

d/dz(dp/dx) = d/dx(dp/dz)

I don't remember learning this in my calculus or differential equations classes unless it was called something else.

 

[Simon Bridge]

Those would be mixed partial derivatives.
Look it up.

The short answer is: almost always.

 

[Charanjit]

Hmm...ok never knew that. Thanks.