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Dagger() * IdentityOperator() now simplifies by default #19783

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Jul 17, 2020
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Dagger() * IdentityOperator() now simplifies by default #19783

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Dagger() * IdentityOperator() now simplifies by default
dhruvmendiratta6 Jul 16, 2020
c528041
Made suggested changes
dhruvmendiratta6 Jul 16, 2020
d91e3fe
Added tests
dhruvmendiratta6 Jul 17, 2020
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10 changes: 9 additions & 1 deletion sympy/physics/quantum/dagger.py
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Original file line number Diff line number Diff line change
Expand Up @@ -2,7 +2,7 @@

from __future__ import print_function, division
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from sympy.core import Expr
from sympy.core import Expr, Mul
from sympy.functions.elementary.complexes import adjoint

__all__ = [
Expand Down Expand Up @@ -85,5 +85,13 @@ def __new__(cls, arg):
return obj
return Expr.__new__(cls, arg)

def __mul__(self, other):
from sympy.physics.quantum import IdentityOperator
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Suggested change

if isinstance(other, IdentityOperator):
return self

return Mul(self,other)
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adjoint.__name__ = "Dagger"
adjoint._sympyrepr = lambda a, b: "Dagger(%s)" % b._print(a.args[0])
2 changes: 1 addition & 1 deletion sympy/physics/quantum/operator.py
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Expand Up @@ -307,7 +307,7 @@ def _print_contents_latex(self, printer, *args):

def __mul__(self, other):

if isinstance(other, Operator):
if isinstance(other, Operator) or isinstance(other, Dagger):
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return other
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Is there a superclass of Operator and Dagger that would make more sense here? Should Dagger be a subclass of Operator?

I don't know the quantum code so well but special casing types like this suggests that things can be better organised somehow.

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I agree things can be better organized. Also: not every functionality is tested properly.

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Is there a superclass of Operator and Dagger that would make more sense here? Should Dagger be a subclass of Operator?

This is exactly what I was thinking and suggested on the mailing list. But while working on it, it turns out if such a change is made print doesn't work properly. print(Dagger(A)) gives A. I think this happens due to calling of _print_contents of Operator. And due to unfamiliarity with the printing module I found it difficult to further look into it

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I think that if Dagger is a subclass of Operator then if you add a _print_Dagger method it will take precedence over _print_Operator.

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Apologies for not being able to reply earlier, I tried overriding _print_contents() and made a separate _print() function for dagger but still it didn't work.

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I tried overriding _print_contents() and made a separate _print() function for dagger but still it didn't work

Can you show us the diff? It would be easier to comment after that. I think it should work if you add a new _print_Dagger() method.


return Mul(self, other)
Expand Down
2 changes: 2 additions & 0 deletions sympy/physics/quantum/tests/test_operator.py
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Expand Up @@ -94,6 +94,8 @@ def test_identity():

assert I * O == O
assert O * I == O
assert I * Dagger(O) == Dagger(O)
assert Dagger(O) * I == Dagger(O)
assert isinstance(I * I, IdentityOperator)
assert isinstance(3 * I, Mul)
assert isinstance(I * x, Mul)
Expand Down