Please Vote: Exercises in TDPL?

Georg Wrede georg.wrede at
Sun May 17 16:46:48 PDT 2009

Bill Baxter wrote:
> On Fri, May 15, 2009 at 7:40 PM, Georg Wrede <georg.wrede at> wrote:
>> Bill Baxter wrote:
>> Incidentally, here, or in D.learn, somebody was asking for symbolic
>> derivation with D templates. I think one of the excercises in SICP was to
>> write a lisp snippet that did just that.
> You're probably thinking of my message about automatic
> differentiation.  Automatic differentiation is not the same as
> symbolic differentiation.   Symbolic differentiation is not really
> very useful in practice since expressions tend to balloon out into
> huge messes.   It also only works on things that are differentiable
> functions.   Automatic differentiation, on the other hand, works on
> code rather than on mathematical functions.   You can run AD on loops
> and other things that symbolic differentiation just doesn't know how
> to handle, and all of this can be done in O(N) where N is the
> complexity of the forward expression.  I posted a bunch of links in
> that other thread that explain the difference in more detail if you'd
> like to know more.

Ah, thanks!

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