oh k. Guess i got to work my problem out differently. It would be nice if i was able to do stuff like that because i am trying to write a very simple code for doing tensor algebra in continuum mechanics. <br><br>Thanks a lot alexei for the prompt and clear clarification.
<br><br><div><span class="gmail_quote">On 11/9/06, <b class="gmail_sendername">Sheplyakov Alexei</b> <<a href="mailto:varg@theor.jinr.ru">varg@theor.jinr.ru</a>> wrote:</span><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
Hello,<br><br>On Thu, Nov 09, 2006 at 07:38:08AM +0530, aravind b wrote:<br>> Please go through this code :<br>><br>><br>> #include <iostream><br>> #include <ginac/ginac.h><br>> using namespace std;
<br>> using namespace GiNaC;<br>><br>> int main()<br>> {<br>> symbol i_sym("i"), j_sym("j"), e("e"), a("a"), b("b") ;<br>> idx i(i_sym, 3), j( j_sym, 3) ; //defining indices i and j
<br>><br>> scalar_products sp;<br>> sp.add( indexed(e, i), indexed(e, j), delta_tensor(i,j) ); // e.i*<br>> e.j = delta_tensor.i.j<br>><br>> cout << (indexed(e,i)*indexed(e,j)).simplify_indexed(sp) <<endl ;
<br>><br>> return 0;<br>> }<br>><br>> does NOT give delta.j.i instead just gives e.i * e.j - why?<br><br>Quoting the manual:<br>"* as a special case of dummy index summation, it can replace scalar<br>
products of two tensors with a user-defined value"<br><br>Since e.i * e.j is not a scalar (it is a tensor of second rank), your<br>code won't work.<br><br>> Basically, i want to define an orthonormal basis vector set {
e.i}.<br><br>I think using `idx' object to enumerate the basis is a bad idea.<br>In general, GiNaC `indexed', `idx' classes are well-suited for 'basis-less'<br>calculations (see <a href="http://www.ginac.de/FAQ.html#matrix_indexed">
http://www.ginac.de/FAQ.html#matrix_indexed</a> to find<br>out why). They don't prevent anyone from doing calculation in scpecific<br>basis, but don't help either.<br><br>> If i have vector_a = indexed(a, i) * indexed(e, i) and
<br>> vector_b = indexed(b, j) * indexed(e, j) ,<br><br>Indexed objects in GiNaC are treated as tensors, so such a vector_a<br>is _not_ really a vector, but instead a scalar.<br><br><br>Best regards,<br> Alexei<br><br>
--<br>All science is either physics or stamp collecting.<br><br><br><br>-----BEGIN PGP SIGNATURE-----<br>Version: GnuPG v1.4.3 (GNU/Linux)<br><br>iQIVAwUBRVLV27L3rFoFceCwAQL3aw//SkchtQFAGdoQkKu+8u9FertudZO9fHFD<br>9KlKaOBOhnvMydZUHBojaEz3HyTXB9KLX6nmRI3F4PwIi8N0zOSX0kzYNP6c43yT
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<br>/5E3E2kOEdwxtrr3I48Z0QBSclJC6eoqnF0T7BTBkV94mVv0cUMxpf+IWSI2DffB<br>jQaSWrzTkjQ=<br>=VrMW<br>-----END PGP SIGNATURE-----<br><br><br>_______________________________________________<br>GiNaC-list mailing list<br><a href="mailto:GiNaC-list@ginac.de">
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