Elegant users forum

Hello,
I am not sure this is a bug but I am struggling with a discrepancy between R16 and etax when using a matrix element.
I am attaching a simple test file below.
In short when I use a mtrix element in a beamline that is generating dispersion I noticed that my dispersion does not match with the R16 computed by the &matrix_output; see mu stdout below.
For this beamline I would expect both value to match. Thanks for any help! -- Philippe.


=====================================================================================
[piot@paris Slits]$ sddsprintout -column=s -column=ElementName -column=etax -column=etay test.twi
Printout for SDDS file test.twi

s ElementName etax etay
m m m
----------------------------------------------------------
0.000000e+00 _BEG_ 0.000000e+00 0.000000e+00
5.000000e-01 D1 0.000000e+00 0.000000e+00
7.920400e-01 DIPOLE1 -5.660879e-02 0.000000e+00
1.292040e+00 D1 -2.529612e-01 0.000000e+00
1.584080e+00 DIPOLE2 -3.016019e-01 0.000000e+00
1.584080e+00 TDC -3.016019e-01 0.000000e+00
2.084080e+00 D2 -3.016019e-01 0.000000e+00
2.374480e+00 SPEC -3.176425e-01 1.082969e-01
3.874480e+00 D3 1.057375e-02 1.350938e+00
[piot@paris Slits]$ sddsprintout -column=s -column=ElementName -column=R16 -column=R36 test.mat
Printout for SDDS file test.mat

s ElementName R16 R36
m m/1 m/1
----------------------------------------------------------
0.000000e+00 _BEG_ 0.000000e+00 0.000000e+00
5.000000e-01 D1 0.000000e+00 0.000000e+00
7.920400e-01 DIPOLE1 -5.660879e-02 0.000000e+00
1.292040e+00 D1 -2.529612e-01 0.000000e+00
1.584080e+00 DIPOLE2 -3.016019e-01 0.000000e+00
1.584080e+00 TDC -2.530818e-01 0.000000e+00
2.084080e+00 D2 -9.129789e-02 0.000000e+00
2.374480e+00 SPEC -2.189457e-03 1.269738e-02
3.874480e+00 D3 4.609148e-01 1.583921e-01


------ test.ele file

Philippe,

This is a bug. The matrix computation is correct but the twiss parameter propagation is not in this particular case.

The problem is that the twiss parameter computation ignores the time coordinate. I'm looking into how to fix it.

--Michael

This was fixed in release 23.1.0. The "local_dispersion" control of twiss_output can be used to change the default behavior. See the manual for details.

--Michael