Increasing number of points in HypoTestInverter AutoScan

When using HypoTestInverter to set upper limits, I’m finding that AutoScan doesn’t run enough points above the expected limit, so the plus 1 sigma and plus 2 sigma bands are very large. If I run a fixed scan, I get more reasonable bands, but of course now I need to know the limits to run the scan in, and the calculated limits are less precise.

How can I increase the number of points run in the auto scan, to get more precise bands?

EDIT: Another peculiarity: the observed (but not expected) limit appears to depend on what I set the POI value to in the alternate model snapshot. Why is this?

I don’t know much about the internals of the HypoTestInverter, but @moneta might be able to help.

Hi,

You can run a fixed scan where you can set the min max, and number of points, or an automatic scan , which does a bisection starting as default from the full variable range. You can change the variable range by using setMin/setMax on the RooRealVar defining the variable range

Concerning your other questions, yes the observed limit should not depend on the POI value of the alternate (background only model). For that model the POI should be fixed to zero. It might then be a side effect of some fit for the full model not working correctly that uses as POI the initial parameter value

Lorenzo

yes the observed limit should not depend on the POI value of the alternate (background only model)

Actually, I had a typo. It was the null model’s POI value I was changing (though specifically, all that matters is whether it’s set to zero, or any non-zero value, so it’s not really a problem).

You can run a fixed scan where you can set the min max, and number of points, or an automatic scan , which does a bisection starting as default from the full variable range. You can change the variable range by using setMin/setMax on the RooRealVar defining the variable range

Can I change the min and max and run a new scan? I tried this, but it seemed to just use the original settings.

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