From fdf77c07df6aa7b37ff9726219a29e50f5185645 Mon Sep 17 00:00:00 2001 From: Ian Hinder Date: Tue, 2 Apr 2013 11:16:05 +0200 Subject: McLachlan_BSSN.m: Add comment to explain confusing situation with advection term for \tilde \Gamma^i in \partial_t B^i equation --- m/McLachlan_BSSN.m | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/m/McLachlan_BSSN.m b/m/McLachlan_BSSN.m index a835560..333b478 100644 --- a/m/McLachlan_BSSN.m +++ b/m/McLachlan_BSSN.m @@ -737,7 +737,9 @@ evolCalc = (Xt[ua] - eta BetaDriver beta[ua]))], dot[B[ua]] -> + ShiftBCoeff (dotXt[ua] - eta BetaDriver B[ua]) - + (* Note that this dotXt[ua] is not yet \partial_t \tilde \Gamma^i, because the + advection term has not yet been added. It is actually + \partial_t \tilde \Gamma^i - \beta^j \partial_j \tilde \Gamma^i *) } }; @@ -788,6 +790,10 @@ advectCalc = + ShiftAdvectionCoeff Upwind[beta[ub], B[ua], lb] + ((1 - ShiftAdvectionCoeff) Upwind[beta[ub], Xt[ua], lb])) + (* Note that the advection term \beta^j \partial_j \tilde \Gamma^i is not + subtracted here when ShiftAdvectionCoefficient == 1 because it was + implicitly subtracted before (see comment in previous calculation of + dot[B[ua]]. *) } }; -- cgit v1.2.3