Elegant users forum

Hi Michael,
I have dispersion measurements (difference orbits at BPMs) in a linac. I would like to fit the eta_x and etap_x at the
start of the line (that contains earth field and correctors) in a way that gives the measured dispersion values at the BPM. One way would be:
-Fit the measured trajectory with dp/p=0 at the start of the line, using MALIN as the optimization parameter. Repeit with dp/p=1%.
The difference between the two fitted trajectories at the start of the line should give me the initial dispersion and dispersion prime values I am seeking.
If am correct, I ask: is there a more straightforward way ?
One more question: am I correct in assuming that the twiss_ouput instruction will give me the lattice functions with the
dipolare perturbations (earth field and correctors) included provided I set "output_at_each_step = 1" ?

Thanks, Max

Max,

The best way to do this is using fitting of the R16 matrix elements. This ensures that dispersion is being computed in terms of the initial energy deviation (note that &twiss_output gives the "local" dispersion, which isn't what you want). You can also use an EMATRIX element to specify and vary the initial dispersion.

I've attached a file giving an example of how to do this.

--Michael