The Lapse describes how much time elapses between two spacial surfaces
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The Shift functions N i describe the tangential shift as you move from the t 0 to t 0+ dt spacial surface
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Choose Lapse and Shift to:
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Avoid Unphysical Singularities (One cannot avoid physical black hole singularity
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Choice of spherical polar coordinates has singularity at radius r=0.
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Keep Numerical Algorithm Stable
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Insure Consistency of Constraints
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