Question: Variable substitution with differentiation

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?

 

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