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Re: Dt@x@1

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On Jun 2, 6:12 pm, Roland Franzius <roland.franz...@uos.de> wrote:
> Am 01.06.2011 10:33, schrieb Chris Chiasson:
>
> > Why does Dt@x@1 return zero? I would expect it to return unevaluated.
>
> The chain rule for Dt acting on a chain of functions of a single
> argument says
>
> Dt@x@1 = x'[1] Dt[1]  ~  Dt[1]=0
>
> Compare
>
> Trace[Dt[x[y[w[u]]], Constants -> {u, v}]] // TreeForm
>
> Trace[Dt[x[y[w[z]]], Constants -> {u, v}]] // TreeForm
>
> to see that Dt[mostinnnerargument]->0 is used as a rule without
> calulating superflous inner derivatives x', y', w' first.
>
> Its of course the simplifying use of those general cancelling rules,
> easy to recognize and to apply, that makes the CAS working at all (in a
> limited collection of cases in finite time ;-( ).
>
> --
>
> Roland Franzius

Thank you for the explanation Roland. I appreciate it. In another
reply, I posted a method to get x[1] to behave as a symbol (i.e. as if
the computer understood x to have SubValues).

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Dt@x@1 Chris Chiasson <chris.chiasson@gmail.com> - 2011-06-01 08:33 +0000
  Re: Dt@x@1 "Nasser M. Abbasi" <nma@12000.org> - 2011-06-01 10:57 +0000
    Re: Dt@x@1 Chris Chiasson <chris.chiasson@gmail.com> - 2011-06-02 11:15 +0000
    Re: Dt@x@1 magma <maderri2@gmail.com> - 2011-06-02 11:14 +0000
    Re: Dt@x@1 Chris Chiasson <chris.chiasson@gmail.com> - 2011-06-02 11:14 +0000
  Re: Dt@x@1 Roland Franzius <roland.franzius@uos.de> - 2011-06-02 23:12 +0000
    Re: Dt@x@1 Chris Chiasson <chris.chiasson@gmail.com> - 2011-06-04 10:20 +0000

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