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From: osman@sprite.DEC (Eric Osman, dtn 283-7484)
Newsgroups: net.math
Subject: rE: Non-linear systems: discontinuous functions
Message-ID: <347@decwrl.UUCP>
Date: Mon, 28-Jan-85 08:55:46 EST
Article-I.D.: decwrl.347
Posted: Mon Jan 28 08:55:46 1985
Date-Received: Wed, 30-Jan-85 05:39:34 EST
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The function f(x) = 1/q or 0 for p/q and irrational respectively is indeed
quite discontinuous.  But please explain to us all what makes it
differentiable ?  I thought only *smoothies* could be differentiated,
since the derivative is a nice tangent line.  Such a line can't be
unique on bumpy or discontinuous functions, can it ?