I'm off of work this week so I'm generally around. As a warning I've been playing around with logpy recently and will probably push that a little bit.
On Fri, Mar 28, 2014 at 4:14 PM, Ondřej Čertík <[email protected]>wrote: > Do you want to do a G+ hangout about this? Looks like there are couple > options to go about this, it might be the fastest to brainstorm this > face to face. > > Ondrej > > On Fri, Mar 28, 2014 at 8:29 AM, Matthew Rocklin <[email protected]> > wrote: > > Maybe tensor indices should be identified as variables/wilds in > unification > > ? Should A(i, j, -j) unify to A(a, b, -b)? > > > > > > On Fri, Mar 28, 2014 at 5:38 AM, F. B. <[email protected]> wrote: > >> > >> The second point concerns unification of tensor, there are some issues > on > >> contracted indices, with some boilerplate > >> > >> from sympy.tensor.tensor import * > >> L = TensorIndexType('L') > >> i0, i1, i2 = tensor_indices('i0:3', L) > >> A = tensorhead('A', [L]*2, [[1]*2]) > >> > >> The arguments > >> > >> >>> A(i0, i1).args > >> (1, (A(L,L),), (i0, i1)) > >> > >> >>> A(i0, -i0).args > >> (1, (A(L,L),), (dummy_index_0, -dummy_index_0)) > >> > >> > >> > >> > >> That is, the third argument is the list of indices, and in the > contracted > >> form the index i0 gets replaced by dummy_index_0, which makes > unification > >> hard: > >> > >> >>> from sympy.unify import * > >> > >> >>> list(unify(A(i0, i1), A(i0, i2), {}, variables=[i2])) > >> [{i2: i1}] > >> >>> list(unify(A(i0, -i0), A(i1, -i1), {}, variables=[i1])) > >> [{}] > >> > >> > >> > >> The second unify expression does not return anything because the > arguments > >> i0 and i1 have been substituted. A possible solution is to keep the > >> arguments of a TensMul as they have been created, and store the > >> dummy_index_0 inside the corresponding TIDS object. > >> > >> A possible implementation of TensorDerivative (by which I mean the > >> derivatives usually employed to get the equation of motions from the > >> Lagrangian in QFT) can simply rely on rewriterule contained in the unify > >> module. > >> > >> The ability to define new objects such as TensorDerivative, > >> PartialDerivative, CovariantDerivative is the primary reason why I want > to > >> make the tensor expression objects just containers, and possible > transfer > >> all index manipulation algorithms to either TIDS or a new object. > >> > >> -- > >> You received this message because you are subscribed to the Google > Groups > >> "sympy" group. > >> To unsubscribe from this group and stop receiving emails from it, send > an > >> email to [email protected]. > >> To post to this group, send email to [email protected]. > >> Visit this group at http://groups.google.com/group/sympy. > >> To view this discussion on the web visit > >> > https://groups.google.com/d/msgid/sympy/0bcab04e-6d84-465e-8fa8-2592b28b8b3c%40googlegroups.com > . > >> > >> For more options, visit https://groups.google.com/d/optout. > > > > > > -- > > You received this message because you are subscribed to the Google Groups > > "sympy" group. > > To unsubscribe from this group and stop receiving emails from it, send an > > email to [email protected]. > > To post to this group, send email to [email protected]. > > Visit this group at http://groups.google.com/group/sympy. > > To view this discussion on the web visit > > > https://groups.google.com/d/msgid/sympy/CAJ8oX-E4QCqars8wyu1fnckpW1Xfaiyk3-FPmvpfX-Sy9KZiHw%40mail.gmail.com > . > > > > For more options, visit https://groups.google.com/d/optout. > > -- > You received this message because you are subscribed to the Google Groups > "sympy" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To post to this group, send email to [email protected]. > Visit this group at http://groups.google.com/group/sympy. > To view this discussion on the web visit > https://groups.google.com/d/msgid/sympy/CADDwiVC2dOYvobCDcjMBySQx8TS-j7peBsxk2NmqKBrMWqRBQQ%40mail.gmail.com > . > For more options, visit https://groups.google.com/d/optout. > -- You received this message because you are subscribed to the Google Groups "sympy" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at http://groups.google.com/group/sympy. To view this discussion on the web visit https://groups.google.com/d/msgid/sympy/CAJ8oX-FPOVMapkw%2Bz%2BLr8Rs%2BZJpJnVzg9c_A%3DSAyB%3D6CKnWozw%40mail.gmail.com. For more options, visit https://groups.google.com/d/optout.
