Analysis Test Scripts: Check <z> and pt about impactx HOT 1 OPEN

Verifying the evolution of the reference particle is a good check. However, in many cases (all the straight magnetic elements), all components of the momentum (including pt) will be unchanged. In the IOTA ring example, (x,y,z,px,py,pz,pt) are all periodic. If we want to exclude the trivial solution, I suggest looking at the reference particle quantities arc length s and the time t, which will always change (unless the lattice has only zero-length elements).

Because the beam particles are defined relative to the reference particle, the expected average position of the particle beam usually does not change more than a small amount (resulting from noise associated with the statistics due to the finite number of particles).

In order to verify that the beam particles have moved, one simple solution is to check that the initial and final values of the second moments are not identical to all digits (as they should not be), but that they agree within the specified tolerance. Another possibility is to check explicitly that the first particle in the distribution has moved to a different position.

from impactx.