[Commits] [svn:einsteintoolkit] IDAnalyticBH/trunk/ (Rev. 175)
knarf at cct.lsu.edu
knarf at cct.lsu.edu
Thu Oct 7 11:42:08 CDT 2010
User: knarf
Date: 2010/10/07 11:42 AM
Added:
/trunk/doc/
Kerr.txt
Modified:
/trunk/doc/
documentation.tex
/trunk/src/
Kerr.c
Log:
correct computation of shift vector in Kerr metric, along with the documentation and a proof that this is right
File Changes:
Directory: /trunk/doc/
======================
File [added]: Kerr.txt
Delta lines: +48 -0
===================================================================
--- trunk/doc/Kerr.txt (rev 0)
+++ trunk/doc/Kerr.txt 2010-10-07 16:42:08 UTC (rev 175)
@@ -0,0 +1,48 @@
+This document shows that the denominator of the definition of shift_phi
+in the code (p2*Sigma) is equal to the denominator of equation (11) in
+Phys. Rev., D54, 1403Â1416
+
+Lines starting with '>' are commands for sagemath, line starting with
+>> are sagemath output, everything else is comments.
+
+
+Variable definition:
+> Sigma,a,r,m,R,Delta,st2,ct2=var('Sigma,a,r,m,R,Delta,st2,ct2')
+
+This is p2*Sigma from the code, st2 being sin^2(theta) = rho^2/R^2:
+
+> code_denom=(a^2+r^2)*Sigma+2*m*a^2*r*st2
+
+Now substitute Sigma, with ct2 being cos^2(theta) = z^2/R^2:
+
+> code_denom=code_denom.substitute(Sigma=r^2+a^2*ct2)
+
+and use that st2+ct2=1:
+
+> code_denom=code_denom.substitute(ct2=1-st2)
+
+Now look at the denominator in the paper:
+
+> paper_denom=(r^2+a^2)^2-a^2*st2*Delta
+
+Substitute Delta:
+
+> paper_denom=paper_denom.substitute(Delta=r^2-2*m*r+a^2)
+
+And look at the difference between code_denom and paper_denom:
+
+> (code_denom-paper_denom).expand()
+>> 0
+
+qed
+
+And here is the notebook as textblock:
+
+sage: Sigma,a,r,m,R,Delta,st2,ct2=var('Sigma,a,r,m,R,Delta,st2,ct2')
+sage: code_denom=(a^2+r^2)*Sigma+2*m*a^2*r*st2
+sage: code_denom=code_denom.substitute(Sigma=r^2+a^2*ct2)
+sage: code_denom=code_denom.substitute(ct2=1-st2)
+sage: paper_denom=(r^2+a^2)^2-a^2*st2*Delta
+sage: paper_denom=paper_denom.substitute(Delta=r^2-2*m*r+a^2)
+sage: (code_denom-paper_denom).expand()
+0
File [modified]: documentation.tex
Delta lines: +1 -1
===================================================================
--- trunk/doc/documentation.tex 2010-07-12 14:50:35 UTC (rev 174)
+++ trunk/doc/documentation.tex 2010-10-07 16:42:08 UTC (rev 175)
@@ -194,7 +194,7 @@
in which case the formulas
\begin{eqnarray}
\alpha & = &\sqrt{\frac{\Delta}{p^2}}, \\
- \beta^\phi & = & -2 m r_k a / p^2,
+ \beta^\phi & = & -2 m r_k a / (p^2 \Sigma),
\end{eqnarray}
where
\begin{equation}
Directory: /trunk/src/
======================
File [modified]: Kerr.c
Delta lines: +1 -1
===================================================================
--- trunk/src/Kerr.c 2010-07-12 14:50:35 UTC (rev 174)
+++ trunk/src/Kerr.c 2010-10-07 16:42:08 UTC (rev 175)
@@ -132,7 +132,7 @@
p2=a_2+r_2-a*beta_phi;
/* drdR=sqrt_Delta/R; */
lapse=sqrt_Delta/sqrt(p2);
- shift_phi=-2*m*rK*a/p2;
+ shift_phi=-2*m*rK*a/(p2*Sigma);
/* Kerr metric in quasi-isotropic coordinates */
/* ds^2=Phi4*(dR^2+R^2*dth^2+R^2*Chi^2*sin(th)^2*dphi^2) */
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