Thanks for the ideas. I will probably go for the second one at least for now.
On 1 November 2012 19:45, Matthew Rocklin <[email protected]> wrote: > If you're willing to keep your index knowledge around separately you can > build a matrix expression and then subs in immutableMatrices > > X, Y = MatrixSymbol('X', 2, 2), MatrixSymbol('Y', 2, 2) > idx = (0, 1) > > expr = (X+Y)*Y > > nx, ny = ImmutableMatrix(...), ImmutableMatrix(...) > > expr.subs({X: nx, Y: ny})[idx[0], idx[1]] > > > On Thu, Nov 1, 2012 at 1:42 PM, Matthew Rocklin <[email protected]> wrote: >> >> Short answer, you can't yet. Current issues are as follows >> >> MatrixExprs doesn't yet support fancy indexing so you'll have to be >> explicit and use p[i, j] and not p[i] --- this could be fixed by improving >> the `__getitem__` method in MatrixExpr >> >> p[i, j] yields a Symbol with the name "%s_ij"%p.name . This object has no >> connection back to the original p. --- this could be fixed by creating some >> sort of Element(Symbol) class. >> >> >> On Thu, Nov 1, 2012 at 1:36 PM, Stefan Krastanov >> <[email protected]> wrote: >>> >>> This is unrelated to the previous question about matrix expressions. >>> >>> How can I do the following >>> >>> >>> >>> p = MatrixSymbol('p', 2, 1) >>> >>> p[0].subs(p, Matrix([5, 6])) >>> 5 >>> >>> p[x].subs(p, Matrix([5, 6])).subs(x, 0) >>> 5 >>> >>> The first one is more important for me than the second one. >>> >>> -- >>> You received this message because you are subscribed to the Google Groups >>> "sympy" group. >>> To post to this group, send email to [email protected]. >>> To unsubscribe from this group, send email to >>> [email protected]. >>> For more options, visit this group at >>> http://groups.google.com/group/sympy?hl=en. >>> >> > > -- > You received this message because you are subscribed to the Google Groups > "sympy" group. > To post to this group, send email to [email protected]. > To unsubscribe from this group, send email to > [email protected]. > For more options, visit this group at > http://groups.google.com/group/sympy?hl=en. -- You received this message because you are subscribed to the Google Groups "sympy" group. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/sympy?hl=en.
