Elegant users forum

Hi All,

I'm tying to optimize the phase advance between two points in a straight section, when I use psix & psiy in the optimization term command elegant gives me the following error message

unknown token: psix
unknown token: psiy

It does not recognize them?, Is it a bug, or am I using the wrong parameter names

Here are my command line
&optimization_term term = psix 0.96 0.001 sene weight = 1 &end
&optimization_term term = psiy 1.03 0.001 sene weight = 1 &end
Thanks in advance

Hisham,

Have you given a twiss_output command to ensure that elegant is computing twiss parameters?

Also, be sure to quote your optimization expression, e.g.,
&optimization_term term = "psix 0.96 0.001 sene" weight = 1 &end

--Michael

Hi Michael,

Yes I did have a twiss command, quoting the optimization equation does not help.
I have attached my files for reference. Thank you

-- Hisham

Hisham,

I don't know why I didn't realize this before, but you need to use nux=psix/2*pi and nuy instead of psix and psiy. Sorry for the confusion.

--Michael

Hi Michael,

Would you consider adding the psix and psiy column for the optimizer? I am having the same trouble.

Best regards,

Weiming

Weiming,

You can just use "nux 2 / pi /" and "nuy 2 / pi /". I can add psix and psiy explicitly if that is really a problem.

--Michael

Hi Michael,

I tried again, it turns out that

Mark#1.nux is equivalent to Mark#1.psix, except a factor of 2pi.

Thanks a lot!

Weiming

I realize this thread is over 10 years old, but I'm having a very similar issue.

I'm trying to constrain the phase advance between two points, it shows up in the optimization routine apparently fine:
MARK-NLAE.02#1.psix MARK-TARG.A2#1.psix 3.35 0.1 selt: 0.000000000000000e+00

As you can see it is zero. In fact it is always zero.

When I try to use the tune instead, it remains zero:
1*(MARK-NLAE.02#1.nux MARK-TARG.A2#1.nux 0.53 0.03 selt): 0.000000000000000e+00

However, after the optimizer is done running I can compute the phase advance manually by reading the twiss file and I get 3.15 (or thereabouts). Clearly that constraint is not being met and I can't figure out why. It should be constrained from below, but it doesn't appear to be.

In order to constrain the phase advance, here is the syntax if marker 1 preceds marker 2:

"Mark#2.psix Mark#1.psix - 0.5 0.1 segt"

It seems to me you have missed a minus operator after the second psix.

Weiming

Ohh wow, I've probably used those functions a hundred times and I just couldn't see that missing minus sign. Thank you!

I guess what is happening is that once the selt function gets all the inputs it needs it ignores the rest of the stack. That would explain why the error wasn't fatal and why the constraint is always satisfied.