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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