Tnx!
I think there is an error in the line (unbalanced paranthesis):
return node.xreplace ({e: S.One, conjugate(e): S.One})*abs(e)**2)
Also, do you know how I can force the factorization of the 2*g to get
2*g(|psi1|**2 + |psi2|**2)?
On Friday, June 6, 2014 10:45:37 AM UTC+2, F. B. wrote:
>
> A better alternative:
>
> In [1]: from sympy import *
>
> In [2]: expr = eval("Add(Mul(Integer(-1), Integer(2), Symbol('g'),
> Symbol('psi^ss_1'), conjugate(Symbol('psi^ss_1'))), Mul(Integer(-1),
> Integer(2), Symbol('g'), Symbol('psi^ss_2'),
> conjugate(Symbol('psi^ss_2'))), Symbol('omega_2'), Mul(Integer(-1),
> Rational(1, 2), Pow(Symbol('m'), Integer(-1)), Pow(Add(Mul(Integer(-1),
> Symbol('k')), Symbol('k_2')), Integer(2))))")
>
> In [3]: from sympy.strategies.traverse import bottom_up
>
> In [4]: from sympy.strategies import chain, rebuild
>
> In [5]: def to_abs (node ):
> ...: if not isinstance(node, Mul):
> ...: return node
> ...: z = Wild ('z')
> ...: w = Wild ('w')
> ...: m = node .match (z * w *conjugate (w))
> ...: if w in m:
> ...: e =m[w]
> ...: return node.xreplace ({e: S.One, conjugate(e): S.
> One})*abs(e)**2)
> ...: return node
> ...:
>
> In [6]: bottom_up(chain(rebuild, to_abs))(expr)
> Out[6]:
> 2
> 2 2 (k + k₂)
> - 2⋅g⋅│ψ_1__ss│ - 2⋅g⋅│ψ_2__ss│ + ω₂ + ─────────
> 4⋅m
>
>
>
> On Friday, June 6, 2014 9:13:15 AM UTC+2, F. B. wrote:
>>
>> As you have a string representation of your object, a non-sympy way is by
>> using string regex:
>>
>> In [1]: expr = eval("Add(Mul(Integer(-1), Integer(2), Symbol('g'),
>> Symbol('psi^ss_1'), conjugate(Symbol('psi^ss_1'))), Mul(Integer(-1),
>> Integer(2), Symbol('g'), Symbol('psi^ss_2'),
>> conjugate(Symbol('psi^ss_2'))), Symbol('omega_2'), Mul(Integer(-1),
>> Rational(1, 2), Pow(Symbol('m'), Integer(-1)), Pow(Add(Mul(Integer(-1),
>> Symbol('k')), Symbol('k_2')), Integer(2))))")
>>
>> In [2]: expr
>> Out[2]:
>> 2
>> _______ _______ (-k + k₂)
>> - 2⋅g⋅ψ_1__ss⋅ψ_1__ss - 2⋅g⋅ψ_2__ss⋅ψ_2__ss + ω₂ - ──────────
>> 2⋅m
>>
>> In [3]: import re
>>
>> In [4]: eval(re.sub(r"(?P<quote>Symbol\('[^']+'\)),
>> +conjugate\((?P=quote)\)", r"abs(\1)**2", srepr(expr)))
>> Out[4]:
>> 2
>> 2 2 (-k + k₂)
>> - 2⋅g⋅│ψ_1__ss│ - 2⋅g⋅│ψ_2__ss│ + ω₂ - ──────────
>> 2⋅m
>>
>> SymPy also has its own system of pattern matching, but it looks like it
>> needs to match whole expressions.
>>
>> On Thursday, June 5, 2014 11:48:17 PM UTC+2, Andrei Berceanu wrote:
>>>
>>> I have the following expression in sympy:
>>>
>>> "Add(Mul(Integer(-1), Integer(2), Symbol('g'), Symbol('psi^ss_1'),
>>> conjugate(Symbol('psi^ss_1'))), Mul(Integer(-1), Integer(2), Symbol('g'),
>>> Symbol('psi^ss_2'), conjugate(Symbol('psi^ss_2'))), Symbol('omega_2'),
>>> Mul(Integer(-1), Rational(1, 2), Pow(Symbol('m'), Integer(-1)),
>>> Pow(Add(Mul(Integer(-1), Symbol('k')), Symbol('k_2')), Integer(2))))"
>>>
>>>
>>> (sorry for the long line, didnt know how else to paste it)
>>>
>>> Anyway, I would like to factor 2g in front of the 2 terms that contain
>>> it (simplify doesnt do it for some reason) and also would like to replace
>>> all occurrences of x*conjugate(x) by abs(x)**2. There are two such
>>> occurrences and I tried to do expr.replace(a*conjugate(a), abs(a)**2)
>>> without any luck.
>>>
>>> Could anyone please help?
>>>
>>> Tnx,
>>> Andrei
>>>
>>
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