My question is similar to the one referenced, but a bit more complicated.

Considering a PDE of order n, I would like it to be collected by the order of differentiation.

A simple example:

simplify(( (3+4*x)*diff(f(x), `$`(x, 2)))+(5+4*y+z)*(diff(f(x), x))+(1+r+y)*f(x))

where the idea is to return to the form prior to simplification, including the sort by differentiation order.

After it is simplified, I can get the coeff of only the highest order derivative, as

Assuming I have a general function f(x). The derivative with respect to x would be: df/dx .

I now want to rescale, which basically means that I want to change x to a*y where a is a parameter (general constant) and y is my new variable.

If I use

subs( x=a*y, df(x)/dx )

I get

d/d(a*y)  f(a*y)

but 'a' should be a parameter, so this should give

1/a * df(a*y)/dy = df(y)/dy

How do I tell that to Maple?

Assuming I have an expression, 'F', I would like to extract from it a factor, 'a', so the expression is displayed as

a*(F/a)

where F/a is a simplified (or expanded or any other displayed form) expression.

As an example:

F:=1 + Q*x² + P*x³

a:=x² / L²

then this will be displayed

x² / L² * ( L² / x² + Q*L² + P*L²*x)