[ET Trac] [Einstein Toolkit] #200: IDAnalyticBH: Kerr initial data not smooth near z-axis

[Einstein Toolkit]

#200: IDAnalyticBH: Kerr initial data not smooth near z-axis
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 Reporter:  bernard.j.kelly@…         |        Type:  defect            
   Status:  new                       |    Priority:  minor             
Milestone:  ET_2010_11                |   Component:  Cactus            
  Version:  ET_2010_11                |    Keywords:  Kerr discontinuity
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 The Kerr initial data (in EinsteinInitialData/IDAnalyticBH/src/Kerr.c) has
 a defect along the z-axis (that is, the spin axis of the hole). The three-
 metric (for instance) is not smooth across this axis, leading to
 discontinuities in second spatial derivatives near there.

 This appears to be due to overly crude safety measures protecting from
 division by zero when calculating this data. Tweaking these measures for
 more self-consistency leads to much smoother behaviour. I'm attaching a
 simple patch that fixes the problem at least for metric_type = physical.

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Ticket URL: <https://trac.einsteintoolkit.org/ticket/200>
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