Add feedback passmethod by lcarver · Pull Request #983 · atcollab/at

lcarver · 2025-09-02T13:49:01Z

Adding a simple passmethod to compute the mean position of the full beam and feedback with a gain.

The feedback takes simply a gain in x,y, and z, and an optional closed_orbit array (6d).

In this module, a closed_orbit is needed to make sure that the feedback is working. But this does not dictate what the closed_orbit is. To account for this, I added the orbit6 into at.simple_ring to allow an appropriate closed_orbit to feedback to to check that it is working.

Tested with mpi and without, all working fine.

Below is an example script.

from mpi4py import MPI
import at
import numpy as np 
import matplotlib.pyplot as plt


comm = MPI.COMM_WORLD


size = comm.Get_size()
rank = comm.Get_rank()
rank0 = rank == 0

plane = 2
gx = 0.0
gy = 0.01
gz = 0
orb = 3.e-3

closed_orbit = np.array([0.0, 0, 0, 0, 0, 0])
closed_orbit[plane] = orb



ring = at.simple_ring(6e9, 844, 992, 0.1, 0.18, 6e6, 8.5e-5, orb6=closed_orbit, tauy=0,  emity=0) #no radiation damping
ring.set_fillpattern(1)
sigma_matrix = at.sigma_matrix(betax=1, betay=1, alphax=0, alphay=0, emitx=100e-12, emity=10e-18, espread=1e-3, blength=3e-3)

nparts = 1000
nturns = 10000


fb = at.Feedback('fb', gx,gy,gz, closed_orbit)
ring.append(fb)


bmon = at.BeamMoments('bmon')
ring.append(bmon)


parts = at.beam(nparts, sigma_matrix)
parts[plane,:] += 1e-3

if rank0:
    all_means_fb = np.zeros((6,nturns))

for i in np.arange(nturns):
    ring.track(parts, in_place=True, refpts=None)
    
    if rank0:
        all_means_fb[:,i] = bmon.means[:,0,0]       

if rank0:
    plt.plot(1e3*all_means_fb[plane,:])
    plt.xlabel('Turn')
    plt.ylabel('y pos [mm]')
    plt.suptitle('CO_y = {:.0f}mm'.format(orb*1e3))
    plt.show()

lcarver · 2025-09-02T13:49:41Z

lcarver · 2025-09-02T14:37:35Z

ready for re-review

lcarver · 2025-09-03T08:10:41Z

ready for re-re-review

lcarver · 2025-09-03T08:37:39Z

Please re-approve. I made a last check of my script and realised I had forgotten to change the GX->Gx in the C, as it is optional it was not doing any damping!

swhite2401 · 2025-09-03T11:02:04Z

Please re-approve. I made a last check of my script and realised I had forgotten to change the GX->Gx in the C, as it is optional it was not doing any damping!

Could you please add unit tests first? Thanks!

Not ready

lcarver · 2026-01-27T13:14:57Z

I added an optional rolling buffer for each plane. Can be used by specifying bufferlength_x/y/z. Then the mean for each turn is added to the buffer and the loop uses the mean of the buffer instead of the one turn mean.

Some points/questions I want to make/ask:

I stole most of the buffer functions from atimplib.c and BeamLoadingCavityPass.c. So now they are repeated, which is clearly not efficient. I think we should consider a new library for C functions relating to buffers and array manipulations. Do you think it is needed?
I am sure there are improvements to be made on the memory handling and the pointer usage in the PassMethod.
At the moment it feeds back directly on the horizontal/vertical/longitudinal position rather than the angle. I plan to change this as I think it is a bit problematic. For sure it works for a lumped model, but there is no reason this cannot be used in a full lattice, so this should be considered.

lcarver · 2026-04-23T15:20:34Z

ready for review, should pass

swhite2401 · 2026-04-24T06:55:32Z

+    def __init__(
+        self,
+        family_name: str,
+        Gxp: float = 0.0,


rename to gpx, gpy

swhite2401 · 2026-04-24T06:55:57Z

+            family_name:     Name of the element
+            Gxp:              Feedback Gain in Horizontal (no units:
+                             damping_time [turns] = 2 / Gx )
+            Gyp:              Feedback Gain in Vertical (no units:


rename here as well

also it is 2/gpx

swhite2401 · 2026-04-24T06:56:36Z

+            closed_orbit:    [xp, yp, dp] - desired angle set points
+                             default = [0, 0, 0]
+            bufferlength_xp: How many turns to use for a rolling
+                             buffer in horizontal?


why a question mark?

In the end the rolling buffer is useful or not?

swhite2401 · 2026-04-24T06:57:08Z

+
+        assert len(closed_orbit)==3, assert_msg
+
+        super().__init__(family_name, Gxp=Gxp, Gyp=Gyp, Gdp=Gdp, closed_orbit=closed_orbit, **kwargs)


rename here as well

swhite2401 · 2026-04-24T06:57:35Z

+        assert_msg = 'closed_orbit must have length 3' + \
+                     'referring to [xp,yp,dp] set points'
+
+        assert len(closed_orbit)==3, assert_msg


Should you raise an AtError?

swhite2401 · 2026-04-24T07:00:06Z

    particle: str | Particle = "relativistic",
-    TimeLag: float | Sequence[float] = 0.0
+    TimeLag: float | Sequence[float] = 0.0,
+    orb6: Sequence[float] = np.zeros(6), 


Why is this needed for feedback?

swhite2401 · 2026-04-24T07:00:45Z

    # (although it is not used for anything else)
-    lin_elem = M66("Linear", m66=Mat66, Length=circumference)
+
+    lin_elem = M66("Linear", m66=Mat66, Length=circumference, T1=-orb6, T2=orb6)


I don't understand why you had to change this

swhite2401 · 2026-04-24T07:01:28Z

+void FeedbackPass(double *r_in, int num_particles, struct elem *Elem)
+{	
+    int c;
+    double mxp[] = {0.0}; // the mean that will be computed


could you change to px, py here as well, thisi s what we use in AT

Lee Carver added 12 commits September 1, 2025 09:56

Add unmodified passmethod from simon

78bbfa0

Add MPI, add mex function

33133ba

Check build

5376147

build

08586f0

build

86d58db

rebuild

a64c751

Wrong Dummy mode

1afef0f

Add orbit to simple_ring

198df6a

Add Feedback element

e93858d

Fix all pointers

087f2f1

Stash

0316aac

remove comments

6a95be2

lcarver requested a review from swhite2401 September 2, 2025 13:50

swhite2401 reviewed Sep 2, 2025

View reviewed changes

Comment thread atintegrators/FeedbackPass.c Outdated

Comment thread atintegrators/FeedbackPass.c Outdated

Comment thread atintegrators/FeedbackPass.c Outdated

Comment thread atintegrators/FeedbackPass.c

Lee Carver and others added 3 commits September 2, 2025 16:17

Better pointers

6e1ec0e

Add optionals

c6b320a

Merge branch 'master' into add_feedback_passmethod

9b1def8

swhite2401 reviewed Sep 2, 2025

View reviewed changes

Lee Carver added 3 commits September 3, 2025 10:02

Change capitals, add Sequence, remove kwaargs, modify help

85d1e88

black

9e51f09

put back kwargs as it is needed for passmethod

f025786

swhite2401 approved these changes Sep 3, 2025

View reviewed changes

Change case in C too

680072d

swhite2401 previously approved these changes Nov 6, 2025

View reviewed changes

swhite2401 self-requested a review January 14, 2026 15:44

Lee Carver added 2 commits January 27, 2026 09:14

merge master

fb5b6df

add buffer to feedback pass

052d1a5

Lee Carver added 3 commits April 23, 2026 13:03

Merge branch 'master' into add_feedback_passmethod

c14d7c5

Checkpoint, but ultimately this is not a good implementation

9d3057c

pass test

5612a56

swhite2401 reviewed Apr 24, 2026

View reviewed changes


		assert len(closed_orbit)==3, assert_msg

		super().__init__(family_name, Gxp=Gxp, Gyp=Gyp, Gdp=Gdp, closed_orbit=closed_orbit, **kwargs)

Conversation

lcarver commented Sep 2, 2025

Uh oh!

lcarver commented Sep 2, 2025

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

lcarver commented Sep 2, 2025

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

lcarver commented Sep 3, 2025

Uh oh!

lcarver commented Sep 3, 2025

Uh oh!

swhite2401 commented Sep 3, 2025

Uh oh!

lcarver commented Jan 27, 2026

Uh oh!

lcarver commented Apr 23, 2026

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

2 participants