Mathematica clear a function's derivative definition

Question

I defined the derivative of a function in Mathematica without defining the function itself, i.e. I have a function definition that looks like this:

y'[x_] := constant * f'[x].

I can't figure out how to clear it out. If I use Clear[y'] or `ClearAll[y'], I get an error message:

ClearAll::ssym: y' is not a symbol or a string.

Clear[y] and ClearAll[y] do nothing to remove the definition of y'.

Any ideas on how I can remove the definition of y'?

Answer 1

This should do what you want:

y'[x_] =.

See Unset. Also see this question for related information.

Answer 2

You can use Remove[y]. For a function name f' is unusual syntax, but it does appear in the documentation for derivative: http://reference.wolfram.com/mathematica/ref/Derivative.html

The derivative name form seems to present a bit of a problem for Information (??), which would usually show attribute information.

y'[x_] := constant*f'[x]
y'[4]
??y

constant f'[4]

Global`y

Remove[y]
??y

Information::notfound : Symbol y not found. >>

y'[4]

y'[4]

But oddly, (and nothing to do with the derivative name form):

Information[y]

Global`y

There is some deeper information about Remove here: https://mathematica.stackexchange.com/questions/4921/what-is-the-story-with-removed-symbols