'Return the absolute magnitude of the w.f., `|\psi(x)|^2`
Examples
>>> from sympy import symbols, pi
>>> from sympy.functions import sqrt, sin
>>> from sympy.physics.quantum.state import Wavefunction
>>> x, L = symbols(\'x,L\', real=True)
>>> n = symbols(\'n\', integer=True)
>>> g = sin(n*pi*x/L)
>>> f = Wavefunction(g, (x, 0, L))
>>> f.prob()
Wavefunction(sin(pi*n*x/L)**2, x)'

def prob(self):

    return Wavefunction((self.expr * conjugate(self.expr)), *self.variables)
