McLachlan does not give a reference for the gauge evolution equations

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Issue #1646 open
Roland Haas created an issue

McLachlan_BSSN.m does not seem to contain any information (eg in evolCalc) that would tell me from which paper the different expressions for the shift and lapse evolution expression are taken from (which may be useful to understand what the different coefficients mean, since parsing the multiple factors of the type XXXFactor * AAA + (1-XXXFactor) * BBB to get either AAA or BBB is confusing).

Keyword: McLachlan

Comments (2)

  1. Ian Hinder
    • changed status to open
    • removed comment

    I believe this is addressed in the rewrite branch. We have not yet switched to the rewrite branch, so I am leaving this ticket open just in case. We should also make sure that the references stay up-to-date (e.g. if the equations are changed, this should be noted in the comment).

  2. Roland Haas reporter
    • removed comment

    No references for the gauge evolution are given in the rewrite code (as of git hash 387e14a) where the relevant Kranc code still reads:

        dotalpha   -> - (harmonicF alpha^harmonicN
                             + trK - IfCCZ4[2 Theta, 0]
                             + alphaDriver (alpha - 1)]),
        dot[alpha] -> (+ dotalpha
                       + IfThen[advectLapse!=0, Upwind[beta[ua], alpha, la], 0]
                       + Dissipation[alpha]),
        (* TODO: add not only advection terms, but full Lie derivatives! *)
        dot[beta[ua]] -> (+ dotbeta[ua]
                          + IfThen[advectShift!=0,
                                   Upwind[beta[ub], beta[ua], lb],
                          + Dissipation[beta[ua]]),
        dot[B[ua]] -> IfB[+ dotXt[ua]
                          + IfThen[fixAdvectionTerms!=0,
                                   Upwind[beta[ub], Xt[ua], lb],
                          - (betaDriverValue
                             (+ B[ua]
                              + IfThen[fixAdvectionTerms!=0 && advectShift!=0,
                                       Upwind[beta[ub], beta[ua], lb] /
                                       (shiftGammaCoeffValue alpha^shiftAlphaPower),
                          + IfThen[fixAdvectionTerms==0 && advectShift!=0,
                                   Upwind[beta[ub], B[ua], lb],
                          + Dissipation[B[ua]],

    ie not reference is given at all.

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