How can one swap elements which come from a function?-CodePudding

So I have defined a class called "Particles":

class Particle:
    def __init__(self, posInit, momInit, spin):
        self.posInit = posInit
        self.momInit = momInit
        self.spin = spin
    def momfT(self, t):
        return self.momInit*(math.cos(t))-self.posInit*(math.sin(t))
    def posfT(self, t):
        return self.posInit*(math.cos(t)) self.momInit*(math.sin(t))

P = [Particle(posInit = i, momInit = j, spin = choice(["up", "down"])) for i,j in zip(Zinitial,Pinitial)]

What I now want to do is switch the positions of the particles if a certain condition is met. So something like the following:

if cond==True:
  P[1].posfT[t], P[2].posfT[t1] = P[2].posfT[t1], P[1].posfT[t]

But the above does not work since I am trying to assign to a function a value.

So I am not sure how to do this?

CodePudding user response：

It seems that you intend to store the position and momentum of your particle over time in posfT and momfT respectfully (edit: I previously thought you wanted only the current position). If so, they should not be methods, but attributes. You should also have separate methods to modify those values as t evolves. I suggest to modify your class like this:

class Particle:
    
    def __init__(self, posInit, momInit, spin):
        self.posInit = posInit
        self.momInit = momInit
        self.spin = spin
        self.momfT = dict()
        self.posfT = dict()
        self.calc_at_time(0)
    
    def calc_at_time(self, t):
        self.momfT[t] = self.momInit*(math.cos(t))-self.posInit*(math.sin(t))
        self.posfT[t] = self.posInit*(math.cos(t)) self.momInit*(math.sin(t))

Note: I am assuming that posfT and momfT are initialized with t=0. I absolutely lack the knowledge to know if this is correct, please check and correct as necessary. I am focusing on code here.

You will then be able to set new positions at time t by calling calc_at_time(t)

t = 1
t1 = 2
P[1].calc_at_time(t)
P[1].calc_at_time(t1)
P[2].calc_at_time(t)
P[2].calc_at_time(t1)

And access the position of P[x] at time t with P[x].posfT[t].

Accordingly, what you're trying to do should now work:

if cond == True:
  P[1].posfT[t], P[2].posfT[t1] = P[2].posfT[t1], P[1].posfT[t]

Meaning: posfT of P[1] at [t] becomes posfT of P[2] at t1, and reciprocally.