Organizing parameters

[danielkallendorf]

Hey,
I was trying to implement a new parameter group for (non-blocking) matter, like a target, detector, wedge, ...
Below is my idea of the description of a rough, 1mm $\mathrm{C}_9\mathrm{H}_10$ scintillator plate.

MatterP:
    thickness: 1E-3
    density: 1.09E3
    matter1:
        element: H
        mass: 1.08
        ratio: 10
    matter2:
        element: C
        mass: 12
        ratio: 9
    defect: 1E-2

And the description for a $7\deg=0.12\mathrm{rad}$ Cu wedge-degrader (an angled piece of copper):

MatterP:
    thickness: 1.28E-2
    density: 8.92E3
    matter1:
        element: Cu
        mass: 63.5
        ratio: 1
    defect: 1E-3
    wedge:
        x-angle: 0.12
        y-angle: 0

Questions:
Do we support parameter sub-groups? If so: How do we describe a parameter of type parameter-group?
Do we have any notation for optional and default values? The parameters of wedge are usually 0 for most matter.
How can I describe an N-dim polynomial in the standard? The thickness might be described as a 2d polynomial coefficients.

Best,
Daniel

[DavidSagan]

My thoughts:

• Yes the standard should support subgroups. Things can get complicated and subgoups are needed to handle this complexity.
• Default values are already used in the standard.
• Using expressions, which would include polynomials, has been discussed and the general feeling is that the standard needs to support them but so far no one has submitted a PR for expressions.
• Specifying the mass seems redundant. Also being able to use a formula like C9-H-O is more compact.

[cemitch99]

@danielkallendorf Would you like to open a PR introducing this feature when/if you are ready?

[DavidSagan]

@danielkallendorf Take a look at the Bmad manual https://www.classe.cornell.edu/bmad/manual.html which has a foil element.