## modulate_elements command

Moderators: cyao, michael_borland

Pradeep
Posts: 14
Joined: 04 Jun 2019, 07:33

### modulate_elements command

I need help to know about the expression of modulation amplitude expressed in RPN in modulate_elements command as follows:

&modulate_elements name = Q, item = TOTAL, expression="3.68e-6 / 5000 / 1 min2 abs" multiplicative=1 differential=0 &end

What is the value of RPN expression "3.68e-6 / 5000 / 1 min2 abs" ? (this modulate_elements command is used in one of example file of elegant, Q is charge)

With regards,
Pradeep Kumar

michael_borland
Posts: 1802
Joined: 19 May 2008, 09:33
Location: Argonne National Laboratory
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### Re: modulate_elements command

Pradeep,

To understand the expression, you should first realize that before the expression is executed, the beam arrival time (Ct) is pushed onto the stack. In the example, T0=3.68e-6 is the revolution time, so "3.68e-6 /" results in the turn number (Ct/T0) being on the top of the stack. We then divide that by 5000 and take the minimum of that result and 1. This gives a function that ramps from 0 to 1 over 5000 turns, then stays at 1.

You can always copy such expressions to the rpn calculator (executed by typing "rpn") and play with them to get better understanding.

--Michael

Pradeep
Posts: 14
Joined: 04 Jun 2019, 07:33

### Re: modulate_elements command

Dear Dr. Michael,

Thanks for kind reply of rpn expression explanation.

With regards,
Pradeep Kumar