Setting quadrupoles strength errors individually

[elafmusa]

I want to insert errors to quadrupoles strengths in a lattice. I am showing here a very simple example for explanation:

Q1 = elements.Quadrupole('Q1', 0.7028, 0.2)
Q2 = elements.Quadrupole('Q2', 0.7028, -0.1)
DRIFT_0 = elements.Drift('DRIFT_0', 7.157399999999999)
ring = [Q1,DRIFT_0, Q2,DRIFT_0,Q1,DRIFT_0,Q2,DRIFT_0,Q1,DRIFT_0, Q2,DRIFT_0,Q1,DRIFT_0,Q2,DRIFT_0,Q1,DRIFT_0, Q2,DRIFT_0,Q1,DRIFT_0,Q2,DRIFT_0]
ring=at.Lattice(ring,energy=1)

errorQ = 1.e-4
tiltQ = 0
shiftQx =0
shiftQy =0
quad_indexes = get_refpts(ring, elements.Quadrupole)
for i in quad_indexes:
print('before err', ring[i].K)
ring[quad_indexes[i]].K += 0.1
print('after err', ring[i].K)

The result of the prints out gives the following:

before err 0.2
after err 0.30000000000000004
before err -0.1
after err -0.1
before err 0.4
after err 0.5
before err -0.1
after err -0.1
before err 0.6
after err 0.7

Whish is not what i want to do, i want to deal with every quadrupole in the lattice individually as in realty i will apply random errors.
So i got for example:

before err 0.2
after err 0.3
before err -0.1
after err 0
before err 0.2
after err 0.3

and so on.

@lfarv

[swhite2401]

Hello @elafmusa, it like looks like you are adding pointers to the same object in your list ring this is why when you change one of them in reality you change all of them. In order to have individual elements you need to add copies instead:

ring = [Q1.deeepcopy(), drift.deepcopy(), etc...