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From: Raffaele Vitolo <raffaele.vitolo@un...>  20100616 16:46:47

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 
From: Thomas Sturm <sturm@re...>  20100616 18:49:35
Attachments:
smime.p7s

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 > >  > ThinkGeek and WIRED's GeekDad team up for the Ultimate > GeekDad Father's Day Giveaway. ONE MASSIVE PRIZE to the > lucky parental unit. See the prize list and enter to win: > http://p.sf.net/sfu/thinkgeekpromo > _______________________________________________ > Reducealgebradevelopers mailing list > Reducealgebradevelopers@... > https://lists.sourceforge.net/lists/listinfo/reducealgebradevelopers  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/ 