Re: [Reduce-algebra-developers] Problem with operators

[Thomas S. <st...@re...>]

Hi Raffaele,

others probably understand the concepts behind the algebraic mode better than I do but here is a hack which might help you to go on:

1: lisp operator setk0;

2: for i := 1:3 do setk0(part({a,b,c},i),i);

3: a;

1

4: b;

2

5: c;

3

This is not really a clean solution though, and I have not checked if it works with arrays on the left hand side.

Thomas


Am 16.06.2010 um 18:26 schrieb Raffaele Vitolo:

> Dear All,
> 
> I am using reduce for computing Hamiltonian operators for partial 
> differential equations (a task which is basically a symmetry 
> computation), and I'm facing the following problem. I have a list of 
> identifiers {ddx,ddy,ddz,...} which are names of vector fields, 
> introduced with a suitable procedure that has been developed by some 
> Dutch researcher almost 20 years ago. In order to define their 
> components I have to write down something like
> ddx(0,1):=...
> ddx(0,2):=...
> ...
> ddx(1,1):=...
> ...
> ddy(0,1):=...
> and so on.
> But reduce is refusing the automatization of the above definitions:
> if I write something like
> 
> for i:=1:3 do
> <<
> for j:=1:n do
> <<
> part({ddx,ddy,ddz},i)(0,j):=...;
>>> ;
>>> ;
> 
> I get an error message
> 
> part({ddx,ddy,ddz},1)(0,1) invalid as assignment
> 
> I get a similar error even if I define a list like ll:={sin} and I
> try to do part(ll,1)(x); the error message is
> part(ll,1) invalid as operator. So I guess that the problem is how to 
> use a list of identifiers as operator names.
> 
> I'm almost sure that I would manage this if I would know lisp, 
> unfortunately I am a newcomer.. I thank you for any explanation you 
> would provide to me for this trivial question.
> 
> Best,
> 
> Raffaele.
> 
> -- 
> Raffaele Vitolo, Dipartimento di Matematica 'E. De Giorgi'
> Universita' del Salento, via per Arnesano 73100 Lecce ITALY
> tel.: +39 0832 297425 (office) fax.: +39 0832 297594
> home page: http://poincare.unisalento.it/vitolo
> 
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-- 
Dr. habil. Thomas Sturm
Departamento de Matematicas, Estadistica y Computacion
Universidad de Cantabria, Santander, Spain
Avda. Los Castros s/n, Room 1072, +34 693 251058
http://personales.unican.es/sturmt/