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Re: Convert from String to variable

• To: mathgroup at smc.vnet.net
• Subject: [mg70247] Re: [mg70229] Convert from String to variable
• From: "Jean-Marc Gulliet" <jeanmarc.gulliet at gmail.com>
• Date: Mon, 9 Oct 2006 01:56:03 -0400 (EDT)
• References: <200610080604.CAA11869@smc.vnet.net> <NDBBJGNHKLMPLILOIPPOAECNFDAA.djmp@earthlink.net> <366c6f340610081232x7f030299lc3f5f5827d3b757e@mail.gmail.com> <366c6f340610081242h1de28809k4dcf80adbfdb81a@mail.gmail.com>

On 10/8/06, Peng Yu <pengyu.ut at gmail.com> wrote:
> Hi,
>
> I replied the mail to mathgroup at smc.vnet.net. It seems that I haven't
> subscribe to that mailing list. So I forward the mail to you. Would
> you please take some time to answer it?
>
> Thanks,
> Peng
>
> ---------- Forwarded message ----------
> From: Peng Yu <pengyu.ut at gmail.com>
To: mathgroup at smc.vnet.net
> Subject: [mg70247] Re: [mg70229] Convert from String to variable
>
>
> On 10/8/06, David Park <djmp at earthlink.net> wrote:
> > Peng,
> >
> > Just use Symbol.
> >
> > Symbol["a" <> ToString[1] <> ToString[2] <> ToString[3]]
> > Head[%]
> > a123
> > Symbol
>
> What I really intent to define is a function like the following. l, m
> and n could go from 0 to any positive integer. Here the parameter list
> of CD should also be changed correspondingly.
>
> CD[Ith_, z_, d_, Ith0_, a000_, a001_, a002_, a010_, a011_, a012_, a020_,
>     a021_, a022_, a100_, a101_, a102_, a110_, a111_, a112_, a120_, a121_,
>     a122_, a200_, a201_, a202_, a210_, a211_, a212_, a220_, a221_, a222_] :=
>     Sum[ToExpression["a" <> ToString[l] <> ToString[m] <> ToString[n]]*(
>     Ith - Ith0)^l*z^(2*m)*d^(n), {l, 0, 2}, {m, 0, 2}, {n, 0, 2}]
>
>
> I tried this, but it is not working. The difficulty is in the left
> hand side. Can I write a function to define a set of other functions?
>
> CD[Ith_, z_, d_, Ith0_, Flatten@
>     Table[ToExpression["a" <> ToString[l] <> ToString[m] <> ToString[n] <>
>            "_"], {l, 0, 2}, {m, 0, 2}, {n, 0, 2}]] := Sum[ToExpression["a" <>
>             ToString[l] <> ToString[m] <> ToString[n]]*(Ith - Ith0)^l*z^(
>           2*m)*d^(n), {l, 0, 2}, {m, 0, 2}, {n, 0, 2}]
>

You should use an immediate assigment '=' rather than a delayed assighment ':='

In[1]:=
CD[Ith_, z_, d_, Ith0_, a000_, a001_, a002_, a010_,
   a011_, a012_, a020_, a021_, a022_, a100_, a101_,
   a102_, a110_, a111_, a112_, a120_, a121_, a122_,
   a200_, a201_, a202_, a210_, a211_, a212_, a220_,
   a221_, a222_] =
  Sum[ToExpression[StringJoin["a", ToString[l],
      ToString[m], ToString[n]]]*(Ith - Ith0)^l*
    z^(2*m)*d^n, {l, 0, 2}, {m, 0, 2}, {n, 0, 2}]

Out[1]=
a000 + a001*d + a002*d^2 + a100*(Ith - Ith0) +
  a101*d*(Ith - Ith0) + a102*d^2*(Ith - Ith0) +
  a200*(Ith - Ith0)^2 + a201*d*(Ith - Ith0)^2 +
  a202*d^2*(Ith - Ith0)^2 + a010*z^2 + a011*d*z^2 +
  a012*d^2*z^2 + a110*(Ith - Ith0)*z^2 +
  a111*d*(Ith - Ith0)*z^2 + a112*d^2*(Ith - Ith0)*
   z^2 + a210*(Ith - Ith0)^2*z^2 +
  a211*d*(Ith - Ith0)^2*z^2 + a212*d^2*(Ith - Ith0)^2*
   z^2 + a020*z^4 + a021*d*z^4 + a022*d^2*z^4 +
  a120*(Ith - Ith0)*z^4 + a121*d*(Ith - Ith0)*z^4 +
  a122*d^2*(Ith - Ith0)*z^4 + a220*(Ith - Ith0)^2*
   z^4 + a221*d*(Ith - Ith0)^2*z^4 +
  a222*d^2*(Ith - Ith0)^2*z^4

HTH,
Jean-Marc

• References:
  • Convert from String to variable
    • From: "PengYu.UT@gmail.com" <PengYu.UT@gmail.com>