Limit of core_shell_cylinder should be exactly the same as hollow_cylinder (Trac #1169)

[butlerpd]

Checking with 4.2, the core_shell_cylinder using an SLD of 6.34 for both the core and solvent and otherwise the same structural parameters SHOULD give the exact same result as the hollow_cylinder using a solvent SLD of 6.34. It is "close" but not the same. In particular the Intensity at q=1E-3 is about 15% different and the oscillations a just a tad off.
the parameters used were:

R_in = 30
R_out = 10
L = 400
background = 0.001
Vol Frac of TOTAL cylinder = 0.05

Not sure if this is just a numerical thing but seems a bit much for that? This needs investigating and possibly fixing

Migrated from http://trac.sasview.org/ticket/1169

{
    "status": "new",
    "changetime": "2018-09-06T11:51:36",
    "_ts": "2018-09-06 11:51:36.158624+00:00",
    "description": "Checking with 4.2, the core_shell_cylinder using an SLD of 6.34 for both the core and solvent and otherwise the same structural parameters SHOULD give the exact same result as the hollow_cylinder using a solvent SLD of 6.34.  It is \"close\" but not the same. In particular the Intensity at q=1E-3 is about 15% different and the oscillations a just a tad off.\nthe parameters used were:\n{{{\nR_in = 30\nR_out = 10\nL = 400\nbackground = 0.001\nVol Frac of TOTAL cylinder = 0.05\n}}} \n\nNot sure if this is just a numerical thing but seems a bit much for that? This needs investigating and possibly fixing",
    "reporter": "butler",
    "cc": "",
    "resolution": "",
    "workpackage": "McSAS Integration Project",
    "time": "2018-09-06T11:51:36",
    "component": "SasView",
    "summary": "Limit of core_shell_cylinder should be exactly the same as hollow_cylinder",
    "priority": "major",
    "keywords": "",
    "milestone": "SasView 4.3.0",
    "owner": "",
    "type": "defect"
}

[butlerpd]

This is a sasmodels issue not a sasview issue so moving it now

[RichardHeenan]

Hollow_cylinder does not have an end cap, core_shell_cylinder does, so the premise that the two should give the same results in the suggested example is not correct, though they may indeed be very similar. Thus I suspect that this is not an issue.

[butlerpd]

excellent point @RichardHeenan it is not clear from the diagrams but if you actually read the fine print in the docs it is stated right there in plain English -- so in this case the core shell version should be more than 10% higher in intensity (so 15 sounds about right). Will close this as a non issue