Ah I forgot to mention something that might be relevant... DifferentialOperator subclasses Operator, which is a subclass of QExpr and thus Expr.
On Wed, Jul 6, 2011 at 1:45 PM, Tomo Lazovich <lazov...@fas.harvard.edu>wrote: > Hi sympy folk, > > I've been writing a new class, DifferentialOperator, in > sympy.physics.quantum. It takes a symbol (or string to sympify) as an > argument, and it is non-commutative (this is all you really need to know for > this discussion). > > At some point when doing representations of momentum operators in a > position basis, we produce an expression like > DiracDelta(x-x_1)*DiracDelta(x_1-x_2)*DifferentialOperator(x_1), where x, > x_1, and x_2 are all symbols. When I try to integrate this over x_1, I get > the output: > > >>> > integrate(DiracDelta(x-x_1)*DiracDelta(x_1-x_2)*DifferentialOperator(x_1), > (x_1, -oo, oo)) > DiracDelta(x - x_2) * DifferentialOperator(oo) > > when we expect instead DiracDelta(x - x_2) * DifferentialOperator(x). > > After some hunting in the code, I think I've isolated this to the behavior > of as_independent, which is called in the process of integration. If you run > > >>> f = DiracDelta(x-x_1)*DiracDelta(x_1-x_2)*DifferentialOperator(x_1) > >>> f.as_independent(x_1) > (DifferentialOperator(x_1), DiracDelta(x - x_1)â‹…DiracDelta(x_1 - x_2)) > > So, even though DifferentialOperator(x_1) depends on x_1 (x_1 appears in > its free_symbols, and has(x_1) returns True) it still gets separated out as > independent > and is thus treated as a coefficient in the integral. > > Does someone who is more familiar with this code know what's going on? Is > this desired behavior because the DifferentialOperator is non-commutative, > or is there a bug in as_independent? > > Thanks for your help! > > Tomo > > -- You received this message because you are subscribed to the Google Groups "sympy" group. To post to this group, send email to sympy@googlegroups.com. To unsubscribe from this group, send email to sympy+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/sympy?hl=en.
