Calculating twiss after adding error to magnets about cpymad

[coldfix]

Hey,

I believe this may be an issue due to the implementation of m.twiss() calling select(clear) under the hood. This is the way it was designed when I initially forked the project, and I'm not sure it's a good thing to do. The solution would be to use instead

m.command.twiss(...)
table = m.get_table('twiss')

Does this help in your case?

[coldfix]

Hey, somehow your answer was deleted.. (?)

I looked at your code, it seems you're using an old unmaintained version of cpymad!

I recommend you use the current version, available in this repo and also on PyPI:

pip install cpymad

With new cpymad, you will have to do some minor replacements:

# OLD SYNTAX:
from cern import cpymad
m = cpymad.start_madx()
m.twiss('bts', fname='twissfile.txt', ...)

becomes

from cpymad import Madx
m = Madx(command_log="commands.madx")
m.twiss('bts', file='twissfile.txt')

This example also incorporates the possibility to forward all executed MAD-X commands to a text file. I recommend doing this in case of trouble, so you can check if the generated MAD-X file can be executed without cpymad and whether incorrect commands have been generated.

Best,
Thomas

[mina-acc]

Hi,
I deleted the post to check the code again and be sure that the output is the same as I reported before. Thanks for your quick response in advance! :)
It seems to work! The MAD-X commands text file was the best source to find the bugs in my code.
Thanks for being so helpful.

Regards,
Mina

[coldfix]

Okay, great. I'll close then.