Editing SSC/Stability/BiPolytropes/RedGiantToPN (section)

===Fixed Interface Pressure===

====Equilibrium Sequence Expressions====

From the relevant [[SSC/Structure/BiPolytropes/Analytic51#Step_5:_Interface_Conditions|interface conditions]], we find,

<table border="0" cellpadding="3" align="center">

<tr>
  <td align="right">
<math>\biggl( \frac{K_e}{K_c} \biggr) </math>
  </td>
  <td align="center">
<math>=</math>
  </td>
  <td align="left">
<math>\rho_0^{-4/5}\biggl( \frac{\mu_e}{\mu_c} \biggr)^{-2} \theta^{-4}_i \, .</math>
  </td>
</tr>
</table>

Inverting this last expression gives,

<table border="0" cellpadding="3" align="center">

<tr>
  <td align="right">
<math>\rho_0^{4/5}</math>
  </td>
  <td align="center">
<math>=</math>
  </td>
  <td align="left">
<math>\biggl( \frac{\mu_e}{\mu_c} \biggr)^{-2} \theta^{-4}_i \biggl( \frac{K_e}{K_c} \biggr)^{-1} </math>
  </td>
</tr>

<tr>
  <td align="right">
<math>\Rightarrow ~~~ \rho_0^{1/5}</math>
  </td>
  <td align="center">
<math>=</math>
  </td>
  <td align="left">
<math>
\biggl[
\biggl( \frac{\mu_e}{\mu_c} \biggr)^{-1 / 2} \theta^{-1}_i \biggl( \frac{K_e}{K_c} \biggr)^{-1 / 4} 
\biggr]
\, .</math>
  </td>
</tr>
</table>

Hence, keeping <math>K_c</math> and <math>K_e</math> constant, we have,

<table border="0" align="center" cellpadding="5">

<tr>
  <td align="right">
<math>M_\mathrm{core} </math>
  </td>
  <td align="center">
<math>=</math>
  </td>
  <td align="left">
<math>\biggl[K_c^{3/2} G^{-3/2}\biggl( \frac{K_e}{K_c} \biggr)^{1 / 4} \biggr]
\biggl[
\biggl( \frac{\mu_e}{\mu_c} \biggr)^{1 / 2} \theta_i  
\biggr]
\biggl(\frac{6}{\pi}\biggr)^{1 / 2} (\xi_i \theta_i)^3
</math>
  </td>
</tr>

<tr>
  <td align="right">
&nbsp;
  </td>
  <td align="center">
<math>=</math>
  </td>
  <td align="left">
<math>
\biggl[K_c^{5}K_e G^{-6}\biggr]^{1 / 4}
\biggl( \frac{\mu_e}{\mu_c} \biggr)^{1 / 2}  
\biggl(\frac{6}{\pi}\biggr)^{1 / 2} \xi_i^3 \theta_i^4
\, ;</math>
  </td>
</tr>

<tr>
  <td align="right">
<math>M_\mathrm{tot} </math>
  </td>
  <td align="center">
<math>=</math>
  </td>
  <td align="left">
<math>
\biggl[K_c^{3/2} G^{-3/2} \biggl( \frac{K_e}{K_c} \biggr)^{1 / 4}\biggr]
\biggl[
\biggl( \frac{\mu_e}{\mu_c} \biggr)^{1 / 2} \theta_i  
\biggr]
\biggl( \frac{\mu_e}{\mu_c} \biggr)^{-2}
\biggl(\frac{2}{\pi}\biggr)^{1 / 2} \frac{A\eta_s}{\theta_i}
</math>
  </td>
</tr>

<tr>
  <td align="right">
&nbsp;
  </td>
  <td align="center">
<math>=</math>
  </td>
  <td align="left">
<math>
\biggl[K_c^{5}K_e G^{-6}\biggr]^{1 / 4}
\biggl( \frac{\mu_e}{\mu_c} \biggr)^{-3/2}
\biggl(\frac{2}{\pi}\biggr)^{1 / 2} A\eta_s
\, ;</math>
  </td>
</tr>

<tr>
  <td align="right">
<math>r_\mathrm{core} </math>
  </td>
  <td align="center">
<math>=</math>
  </td>
  <td align="left">
<math>
\biggl[K_e G^{-1} \biggr]^{1 / 2} 
\biggl( \frac{\mu_e}{\mu_c} \biggr)  
\biggl( \frac{3}{2\pi}\biggr)^{1 / 2} \xi_i \theta_i^2
\, ;
</math>
  </td>
</tr>

<tr>
  <td align="right">
<math>R </math>
  </td>
  <td align="center">
<math>=</math>
  </td>
  <td align="left">
<math>
\biggl[K_e G^{-1} \biggr]^{1/2}
\frac{\eta_s}{\sqrt{2\pi}}
\, ;
</math>
  </td>
</tr>

<tr>
  <td align="right">
<math>\rho_0</math>
  </td>
  <td align="center">
<math>=</math>
  </td>
  <td align="left">
<math>
\biggl[ \frac{K_e}{K_c} \biggr]^{-5 / 4} 
\biggl( \frac{\mu_e}{\mu_c} \biggr)^{-5 / 2}  \theta_i^{-5}
\, ;</math>
  </td>
</tr>

<tr>
  <td align="right">
<math>P_i</math>
  </td>
  <td align="center">
<math>=</math>
  </td>
  <td align="left">
<math>
\biggl[ K_c \biggr] \biggl[ \biggl( \frac{\mu_e}{\mu_c} \biggr)^{-3} \theta^{-6}_i \biggl( \frac{K_e}{K_c} \biggr)^{-3/2}\biggr] \theta_i^6
</math>
  </td>
</tr>

<tr>
  <td align="right">
&nbsp;
  </td>
  <td align="center">
<math>=</math>
  </td>
  <td align="left">
<math>
\biggl[ K_c^{5}K_e^{-3} \biggr]^{1 / 2}  
\biggl( \frac{\mu_e}{\mu_c} \biggr)^{-3} \, .
</math>
  </td>
</tr>
</table>
This last expression shows that <font color="red"><b>if <math>K_c</math> and <math>K_e</math> are both held fixed, then the interface pressure, <math>P_i</math>, will be constant</b></font> along the sequence of equilibrium models.

Note also:

<table border="0" align="center" cellpadding="5">

<tr>
  <td align="right">
<math>\nu \equiv \frac{M_\mathrm{core}}{M_\mathrm{tot}} </math>
  </td>
  <td align="center">
<math>=</math>
  </td>
  <td align="left">
<math>
\biggl\{
\biggl[K_c^{5}K_e G^{-6}\biggr]^{1 / 4}
\biggl( \frac{\mu_e}{\mu_c} \biggr)^{1 / 2}  
\biggl(\frac{6}{\pi}\biggr)^{1 / 2} \xi_i^3 \theta_i^4
\biggr\}
\biggl\{
\biggl[K_c^{5}K_e G^{-6}\biggr]^{1 / 4}
\biggl( \frac{\mu_e}{\mu_c} \biggr)^{-3/2}
\biggl(\frac{2}{\pi}\biggr)^{1 / 2} A\eta_s
\biggr\}^{-1}
</math>
  </td>
</tr>

<tr>
  <td align="right">
&nbsp;
  </td>
  <td align="center">
<math>=</math>
  </td>
  <td align="left">
<math>
\biggl( \frac{\mu_e}{\mu_c} \biggr)^{2}  
\frac{\sqrt{3}\xi_i^3 \theta_i^4}{A\eta_s}
\, ;
</math>
  </td>
</tr>

<tr>
  <td align="right">
<math>q \equiv \frac{r_\mathrm{core}}{R} </math>
  </td>
  <td align="center">
<math>=</math>
  </td>
  <td align="left">
<math>
\biggl\{
\biggl[K_e G^{-1} \biggr]^{1 / 2} 
\biggl( \frac{\mu_e}{\mu_c} \biggr)  
\biggl( \frac{3}{2\pi}\biggr)^{1 / 2} \xi_i \theta_i^2
\biggr\}
\biggl\{
\biggl[K_e G^{-1} \biggr]^{1/2}
\frac{\eta_s}{\sqrt{2\pi}}
\biggr\}^{-1}
</math>
  </td>
</tr>

<tr>
  <td align="right">
&nbsp;
  </td>
  <td align="center">
<math>=</math>
  </td>
  <td align="left">
<math>
\biggl( \frac{\mu_e}{\mu_c} \biggr)  
\frac{ \sqrt{3}\xi_i \theta_i^2 }{\eta_s}
\, .
</math>
  </td>
</tr>
</table>

====Fixed Interface Pressure Sequence Plots====
A plot of <math>M_\mathrm{tot}~\biggl[K_c^{5}K_e G^{-6}\biggr]^{-1 / 4}</math> versus <math>R~\biggl[K_e G^{-1} \biggr]^{-1/2}</math> at <font color="red"><b>fixed interface pressure</b></font> will be generated via the relations,
<table align="center" cellpadding="8">
<tr>
  <td align="center">Ordinate: <math>M_\mathrm{tot}</math></td>
  <td align="center">&nbsp;</td>
  <td align="center">Abscissa: <math>R</math></td>
</tr>

<tr>
  <td align="center">
<math>\biggl( \frac{\mu_e}{\mu_c} \biggr)^{-3/2}
\biggl(\frac{2}{\pi}\biggr)^{1 / 2} A\eta_s
</math>
  </td>
  <td align="center">
'''vs'''
  </td>
  <td align="center">
<math>\frac{\eta_s}{\sqrt{2\pi}} \, .</math>
  </td>
</tr>
</table>

Alternatively, a plot of <math>M_\mathrm{tot}~\biggl[K_c^{5}K_e G^{-6}\biggr]^{-1 / 4}</math> versus <math>\log_{10}(\rho_0) ~\biggl[ \frac{K_e}{K_c} \biggr]^{5 / 4}</math> at fixed interface pressure will be generated via the relations,
<table align="center" cellpadding="8">
<tr>
  <td align="center">Ordinate: <math>M_\mathrm{tot}</math></td>
  <td align="center">&nbsp;</td>
  <td align="center">Abscissa:  <math>\log_{10}(\rho_0)</math></td>
</tr>

<tr>
  <td align="center">
<math>\biggl( \frac{\mu_e}{\mu_c} \biggr)^{-3/2}
\biggl(\frac{2}{\pi}\biggr)^{1 / 2} A\eta_s
</math>
  </td>
  <td align="center">
'''vs'''
  </td>
  <td align="center">
<math> 
\log_{10}\biggl[\biggl( \frac{\mu_e}{\mu_c} \biggr)^{-5 / 2}  \theta_i^{-5}\biggr]
</math>
  </td>
</tr>
</table>

<table border="1" align="center" cellpadding="8"><tr><td align="left">

The expression for <math>dM_\mathrm{tot}/d\ell_i</math> is &hellip;
<table align="center" cellpadding="8">

<tr>
  <td align="right">
<math>\biggl[K_c^{5}K_e G^{-6}\biggr]^{-1 / 4}
\frac{dM_\mathrm{tot}}{d\ell_i}</math>
</td>
  <td align="center"><math>=</math></td>
  <td align="left">
<math>
\biggl( \frac{\mu_e}{\mu_c} \biggr)^{-3/2} \biggl(\frac{2}{\pi}\biggr)^{1 / 2} 
~\frac{d}{d\ell_i} \biggl[
A\eta_s
\biggr]
</math>
  </td>
</tr>

<tr>
  <td align="right">&nbsp;</td>
  <td align="center"><math>=</math></td>
  <td align="left">
<math>
\biggl( \frac{\mu_e}{\mu_c} \biggr)^{-3/2} \biggl(\frac{2}{\pi}\biggr)^{1 / 2} 
~\frac{d}{d\ell_i} \biggl[
A\eta_s
\biggr]
</math>
  </td>
</tr>

<tr>
  <td align="right">
&nbsp;
  </td>
  <td align="center">
<math>=</math>
  </td>
  <td align="left">
<math>
\biggl( \frac{\mu_e}{\mu_c} \biggr)^{-3/2} \biggl(\frac{2}{\pi}\biggr)^{1 / 2} 
~\frac{d}{d\ell_i} \biggl\{
\biggl[ \frac{1 + (1-m_3)^2 \ell_i^2 }{ 1+\ell_i^2 }\biggr]^{1 / 2} \biggl[ \frac{\pi}{2} + \eta_i + \tan^{-1}(\Lambda_i) \biggr]
\biggr\} 
</math>
  </td>
</tr>

<tr>
  <td align="right">
<math>\Rightarrow ~~~ \biggl( \frac{\mu_e}{\mu_c} \biggr)^{3/2} \biggl(\frac{2}{\pi}\biggr)^{-1 / 2} 
\biggl[K_c^{5}K_e G^{-6}\biggr]^{-1 / 4}
\frac{dM_\mathrm{tot}}{d\ell_i}</math>
  </td>
  <td align="center">
<math>=</math>
  </td>
  <td align="left">
<math>
\frac{1}{2}\biggl[ \frac{\pi}{2} + \eta_i + \tan^{-1}(\Lambda_i) \biggr]
\biggl[ \frac{1 + (1-m_3)^2 \ell_i^2 }{ 1+\ell_i^2 }\biggr]^{- 1 / 2} 
~\frac{d}{d\ell_i} \biggl\{
\biggl[ \frac{1 + (1-m_3)^2 \ell_i^2 }{ 1+\ell_i^2 }\biggr] 
\biggr\} 
</math>
  </td>
</tr>

<tr>
  <td align="right">
&nbsp;
  </td>
  <td align="center">
&nbsp;
  </td>
  <td align="left">
<math>
+ 
\biggl[ \frac{1 + (1-m_3)^2 \ell_i^2 }{ 1+\ell_i^2 }\biggr]^{1 / 2} \biggl\{
\frac{d\eta_i}{d\ell_i}
\biggr\} 
+ 
\biggl[ \frac{1 + (1-m_3)^2 \ell_i^2 }{ 1+\ell_i^2 }\biggr]^{1 / 2} \biggl\{\frac{d}{d\ell_i}
\biggl[ \tan^{-1}(\Lambda_i) \biggr]
\biggr\} 
</math>
  </td>
</tr>

<tr>
  <td align="right">
&nbsp;
  </td>
  <td align="center">
<math>=</math>
  </td>
  <td align="left">
<math>
\frac{1}{2}\biggl[ \frac{\pi}{2} + \eta_i + \tan^{-1}(\Lambda_i) \biggr]
\biggl[ \frac{1 + (1-m_3)^2 \ell_i^2 }{ 1+\ell_i^2 }\biggr]^{- 1 / 2} 
~\frac{d}{d\ell_i} \biggl\{
\biggl[ \frac{1 + (1-m_3)^2 \ell_i^2 }{ 1+\ell_i^2 }\biggr] 
\biggr\} 
</math>
  </td>
</tr>

<tr>
  <td align="right">
&nbsp;
  </td>
  <td align="center">
&nbsp;
  </td>
  <td align="left">
<math>
+ 
\biggl[ \frac{1 + (1-m_3)^2 \ell_i^2 }{ 1+\ell_i^2 }\biggr]^{1 / 2} \biggl\{
\frac{d}{d\ell_i} \biggl[ m_3 \biggl( \frac{\ell_i}{1+\ell_i^2}\biggr) \biggr]
\biggr\} 
+ 
\biggl[ \frac{1 + (1-m_3)^2 \ell_i^2 }{ 1+\ell_i^2 }\biggr]^{1 / 2} 
\biggl[ \frac{1}{1+\Lambda_i^2}\biggr] \cdot \frac{d\Lambda_i}{d\ell_i} 
</math>
  </td>
</tr>
</table>

The extremum in <math>M_\mathrm{tot}</math> occurs when the LHS of this expression is zero, that is, when  &hellip;
<table align="center" cellpadding="8">

<table border="0" align="center" cellpadding="5">

<tr>
  <td align="right">
<math>\eta_i</math>
  </td>
  <td align="center">
<math>=</math>
  </td>
  <td align="left">
<math>
m_3 \ell_i (1+\ell_i^2)^{-1}
</math>
  </td>
</tr>

<tr>
  <td align="right">
<math>\Lambda_i</math>
  </td>
  <td align="center">
<math>=</math>
  </td>
  <td align="left">
<math>
\frac{[ 1+ (1 - m_3)\ell_i^2]}{m_3 \ell_i} 
</math>
  </td>
</tr>

<tr>
  <td align="right">
<math>(1+\Lambda_i^2)^{-1}</math>
  </td>
  <td align="center">
<math>=</math>
  </td>
  <td align="left">
<math>
\frac{m_3^2 \ell_i^2}{(1+\ell_i^2)} \biggl[ 1 + (1-m_3)^2 \ell_i^2 \biggr]^{-1} 
</math>
  </td>
</tr>

<tr>
  <td align="right">
<math> 
2\biggl[ \frac{1 + (1-m_3)^2 \ell_i^2 }{ 1+\ell_i^2 }\biggr]^{1 / 2} \biggl\{
\frac{d}{d\ell_i} \biggl[ m_3 \biggl( \frac{\ell_i}{1+\ell_i^2}\biggr) \biggr]
\biggr\} 
+ 
2\biggl[ \frac{1 + (1-m_3)^2 \ell_i^2 }{ 1+\ell_i^2 }\biggr]^{1 / 2} 
\biggl[ \frac{1}{1+\Lambda_i^2}\biggr] \cdot \frac{d\Lambda_i}{d\ell_i} 
</math>
  </td>
  <td align="center">
<math>=</math>
  </td>
  <td align="left">
<math>
-~\biggl[ \frac{\pi}{2} + \eta_i + \tan^{-1}(\Lambda_i) \biggr]
\biggl[ \frac{1 + (1-m_3)^2 \ell_i^2 }{ 1+\ell_i^2 }\biggr]^{- 1 / 2} 
~\frac{d}{d\ell_i} \biggl\{
\biggl[ \frac{1 + (1-m_3)^2 \ell_i^2 }{ 1+\ell_i^2 }\biggr] 
\biggr\} 
</math>
  </td>
</tr>

<tr>
  <td align="right">
<math> \Rightarrow ~~~
2 m_3\biggl[ \frac{1 + (1-m_3)^2 \ell_i^2 }{ 1+\ell_i^2 }\biggr]^{1 / 2} 
\frac{d}{d\ell_i} \biggl\{ \ell_i (1 + \ell_i^2)^{-1}
\biggr\} 
+ 
\frac{2}{m_3}\biggl[ \frac{1 + (1-m_3)^2 \ell_i^2 }{ 1+\ell_i^2 }\biggr]^{1 / 2}
\biggl[ \frac{1}{1+\Lambda_i^2}\biggr] \cdot \frac{d}{d\ell_i}\biggl\{ \ell_i^{-1} \biggl[ 1+ (1 - m_3)\ell_i^2 \biggr]\biggr\} 
</math>
  </td>
  <td align="center">
<math>=</math>
  </td>
  <td align="left">
<math>
-~\biggl[ \frac{\pi}{2} + \eta_i + \tan^{-1}(\Lambda_i) \biggr]
\biggl[ \frac{1 + (1-m_3)^2 \ell_i^2 }{ 1+\ell_i^2 }\biggr]^{- 1 / 2} 
~\frac{d}{d\ell_i} \biggl\{ (1+\ell_i^2)^{-1}
\biggl[1 + (1-m_3)^2 \ell_i^2 \biggr]  
\biggr\} 
</math>
  </td>
</tr>

<tr>
  <td align="right">
<math> \Rightarrow ~~~
2 m_3\biggl[ \frac{1 + (1-m_3)^2 \ell_i^2 }{ 1+\ell_i^2 }\biggr] 
\biggl\{ (1 + \ell_i^2)^{-1} - 2\ell_i^2 (1 + \ell_i^2)^{-2}
\biggr\} 
+ 
\frac{2}{m_3}\biggl[ \frac{1 + (1-m_3)^2 \ell_i^2 }{ 1+\ell_i^2 }\biggr]
\biggl[ \frac{1}{1+\Lambda_i^2}\biggr] 
\biggl\{ -\ell_i^{-2} \biggl[ 1+ (1 - m_3)\ell_i^2 \biggr] + \biggl[ 2(1 - m_3) \biggr]\biggr\} 
</math>
  </td>
  <td align="center">
<math>=</math>
  </td>
  <td align="left">
<math>
-~\biggl[ \frac{\pi}{2} + \eta_i + \tan^{-1}(\Lambda_i) \biggr] 
~\biggl\{ 
-2\ell_i (1+\ell_i^2)^{-2}\biggl[1 + (1-m_3)^2 \ell_i^2 \biggr]  
+
(1+\ell_i^2)^{-1}\biggl[2\ell_i(1-m_3)^2  \biggr]  
\biggr\} 
</math>
  </td>
</tr>

<tr>
  <td align="right">
<math> \Rightarrow ~~~
2 m_3\biggl[ \frac{1 + (1-m_3)^2 \ell_i^2 }{ (1+\ell_i^2)^3 }\biggr] 
\biggl\{ (1 + \ell_i^2) - 2\ell_i^2 \biggr\} 
+ 
\frac{2}{m_3}\biggl[ \frac{1 + (1-m_3)^2 \ell_i^2 }{ 1+\ell_i^2 }\biggr]
\frac{m_3^2 \ell_i^2}{(1+\ell_i^2)} \biggl[ 1 + (1-m_3)^2 \ell_i^2 \biggr]^{-1} 
\biggl\{ -\ell_i^{-2} \biggl[ 1+ (1 - m_3)\ell_i^2 \biggr] + \biggl[ 2(1 - m_3) \biggr]\biggr\} 
</math>
  </td>
  <td align="center">
<math>=</math>
  </td>
  <td align="left">
<math>
-~(1+\ell_i^2)^{-2}\biggl[ \frac{\pi}{2} + \eta_i + \tan^{-1}(\Lambda_i) \biggr] 
~\biggl\{ 
-2\ell_i \biggl[1 + (1-m_3)^2 \ell_i^2 \biggr]  
+
(1+\ell_i^2)\biggl[2\ell_i(1-m_3)^2  \biggr]  
\biggr\} 
</math>
  </td>
</tr>

<tr>
  <td align="right">
<math> \Rightarrow ~~~
2 m_3\biggl[ \frac{1 + (1-m_3)^2 \ell_i^2 }{ (1+\ell_i^2) }\biggr] 
\biggl\{ (1 + \ell_i^2) - 2\ell_i^2 \biggr\} 
+ 
2m_3
\biggl\{ - \biggl[ 1+ (1 - m_3)\ell_i^2 \biggr] + \biggl[ 2(1 - m_3)\ell_i^2 \biggr]\biggr\} 
</math>
  </td>
  <td align="center">
<math>=</math>
  </td>
  <td align="left">
<math>
-~\biggl[ \frac{\pi}{2} + \eta_i + \tan^{-1}(\Lambda_i) \biggr] 
~\biggl\{ 
-2\ell_i \biggl[1 + (1-m_3)^2 \ell_i^2 \biggr]  
+
(1+\ell_i^2)\biggl[2\ell_i(1-m_3)^2  \biggr]  
\biggr\} 
</math>
  </td>
</tr>

<tr>
  <td align="right">
<math> \Rightarrow ~~~
2 m_3 \biggl[ 1 + (1-m_3)^2 \ell_i^2 \biggr] 
\biggl[ \frac{(1 - \ell_i^2)}{(1+\ell_i^2) }\biggr] 
+ 
2m_3
\biggl[ - 1 + (1 - m_3)\ell_i^2 \biggr] 
</math>
  </td>
  <td align="center">
<math>=</math>
  </td>
  <td align="left">
<math>
-~\biggl[ \frac{\pi}{2} + \eta_i + \tan^{-1}(\Lambda_i) \biggr] 
~\biggl\{ 
\biggl[-2 \ell_i -2 (1-m_3)^2 \ell_i^3 \biggr]  
+
\biggl[2\ell_i(1-m_3)^2  \biggr]  
+
\biggl[2(1-m_3)^2 \ell_i^3 \biggr]  
\biggr\} 
</math>
  </td>
</tr>

<tr>
  <td align="right">
<math> \Rightarrow ~~~
\frac{2 m_3 }{(1+\ell_i^2) }\biggl\{
\biggl[ 1 + (1-m_3)^2 \ell_i^2 \biggr] 
\biggl[ (1 - \ell_i^2)\biggr] 
+ 
(1 + \ell_i^2)\biggl[ - 1 + (1 - m_3)\ell_i^2 \biggr] 
\biggr\}
</math>
  </td>
  <td align="center">
<math>=</math>
  </td>
  <td align="left">
<math>
\biggl[ \frac{\pi}{2} + \eta_i + \tan^{-1}(\Lambda_i) \biggr] 
~\biggl\{ 1 - (1-m_3)^2   \biggr\} 2 \ell_i
</math>
  </td>
</tr>

<tr>
  <td align="right">
<math> \Rightarrow ~~~
\frac{2 m_3 }{(1+\ell_i^2) }\biggl\{
\biggl[ 1 + (1-m_3)^2 \ell_i^2 \biggr] 
- \ell_i^2\biggl[ 1 + (1-m_3)^2 \ell_i^2 \biggr] 
+ 
\biggl[ - 1 + (1 - m_3)\ell_i^2 \biggr] 
+ 
\ell_i^2 \biggl[ - 1 + (1 - m_3)\ell_i^2 \biggr] 
\biggr\}
</math>
  </td>
  <td align="center">
<math>=</math>
  </td>
  <td align="left">
<math>
\biggl[ \frac{\pi}{2} + \eta_i + \tan^{-1}(\Lambda_i) \biggr] 
~(2 - m_3)  2m_3 \ell_i
</math>
  </td>
</tr>

<tr>
  <td align="right">
<math> \Rightarrow ~~~
(1+\ell_i^2)^{-1}\biggl\{
1 + (1-m_3)^2 \ell_i^2 
-\ell_i^2 - (1-m_3)^2 \ell_i^4  
- 1 + (1 - m_3)\ell_i^2 
- \ell_i^2  + (1 - m_3)\ell_i^4  
\biggr\}
</math>
  </td>
  <td align="center">
<math>=</math>
  </td>
  <td align="left">
<math>
\biggl[ \frac{\pi}{2} + \eta_i + \tan^{-1}(\Lambda_i) \biggr] 
~(2 - m_3)  \ell_i
</math>
  </td>
</tr>

<tr>
  <td align="right">
<math> \Rightarrow ~~~
\frac{1}{(1+\ell_i^2)(2 - m_3)  \ell_i}\biggl\{
\biggl[ m_3 - 3  \biggr]m_3\ell_i^2 
+ \biggl[1 - m_3 \biggr]m_3\ell_i^4  
\biggr\}
</math>
  </td>
  <td align="center">
<math>=</math>
  </td>
  <td align="left">
<math>
\biggl[ \frac{\pi}{2} + \eta_i + \tan^{-1}(\Lambda_i) \biggr] 
</math>
  </td>
</tr>

<tr>
  <td align="right">
<math> \Rightarrow ~~~
\frac{m_3 \ell_i}{(1+\ell_i^2)(2 - m_3) }\biggl[
( m_3 - 3 ) + (1 - m_3 )\ell_i^2  
\biggr]
</math>
  </td>
  <td align="center">
<math>=</math>
  </td>
  <td align="left">
<math>
\biggl[ \frac{\pi}{2} + \eta_i + \tan^{-1}(\Lambda_i) \biggr] 
</math>
  </td>
</tr>

<!-- BEGIN HIDE
<tr><td align="center" colspan="3"><b>HERE</b></td></tr>
<tr>
  <td align="right">
<math> \Rightarrow ~~~
2 m_3\biggl[ 1 + (1-m_3)^2 \ell_i^2 \biggr]
+ 
2m_3 \biggl\{ -1 - (1 - m_3)\ell_i^2  +  2(1 - m_3)\ell_i^2\biggr\} 
</math>
  </td>
  <td align="center">
<math>=</math>
  </td>
  <td align="left">
<math>
-~\biggl[ \frac{\pi}{2} + \eta_i + \tan^{-1}(\Lambda_i) \biggr] 
~\biggl\{ 
\biggl[-2 \ell_i -2 (1-m_3)^2 \ell_i^3 \biggr]  
+
(1+\ell_i^2)\biggl[2\ell_i(1-m_3)^2  \biggr]  
\biggr\} 
</math>
  </td>
</tr>

<tr>
  <td align="right">
<math> \Rightarrow ~~~
2 m_3\biggl\{ 
1 + (1-m_3)^2 \ell_i^2 
-1 +  (1 - m_3)\ell_i^2\biggr\} 
</math>
  </td>
  <td align="center">
<math>=</math>
  </td>
  <td align="left">
<math>
-~2 \ell_i\biggl[ \frac{\pi}{2} + \eta_i + \tan^{-1}(\Lambda_i) \biggr] 
~\biggl\{ -1  + 2(1-m_3)^2    \biggr\} 
</math>
  </td>
</tr>

<tr>
  <td align="right">
<math> \Rightarrow ~~~
m_3 (2-m_3)  (1 - m_3)\ell_i
</math>
  </td>
  <td align="center">
<math>=</math>
  </td>
  <td align="left">
<math>
-~\biggl[ \frac{\pi}{2} + \eta_i + \tan^{-1}(\Lambda_i) \biggr] 
~\biggl[ 2(1-m_3)^2 - 1   \biggr] 
</math>
  </td>
</tr>

<tr>
  <td align="right">
<math> \Rightarrow ~~~
\frac{m_3 (2-m_3)  (1 - m_3)}{[1 -  2(1-m_3)^2 ]}
</math>
  </td>
  <td align="center">
<math>=</math>
  </td>
  <td align="left">
<math>
\frac{1}{\ell_i}\biggl[ \frac{\pi}{2} + \eta_i + \tan^{-1}(\Lambda_i) \biggr] 
~ 
</math>
  </td>
</tr>

<tr>
  <td align="right">
&nbsp;
  </td>
  <td align="center">
<math>=</math>
  </td>
  <td align="left">
<math>
\frac{1}{\ell_i}\bigg\{
\frac{\pi}{2} + m_3 \ell_i (1+\ell_i^2)^{-1} 
+ \tan^{-1}\biggl[\frac{[ 1+ (1 - m_3)\ell_i^2]}{m_3 \ell_i} \biggr] \biggr\} 
</math>
  </td>
</tr>
END HIDE -->

</table>

For <math>\mu_e/\mu_c = 1.00</math> the <font color="red">solution to this expression is <math>\xi_i = 1.668462981</math></font>.
</td></tr></table>
 

----

<table border="0" align="center" cellpadding="8"><tr><td align="left">
[[File:DataFileButton02.png|right|60px|file = Dropbox/WorkFolder/Wiki edits/BiPolytrope/TwoFirstOrderODEs/Bipolytrope51New.xlsx --- worksheet = SequenceMuRatio100]]Example data values drawn from worksheet "SequenceMuRatio100" &hellip;
<div align="left">
<math>\Delta \xi = (9.01499598 - 0.05)/99 = 0.0905551</math>
</div>

<table border="1" align="center" cellpadding="3">
<tr>
  <td align="center"><math>n_\mathrm{grid}</math></td>
  <td align="center"><math> \xi_i=0.05 + (n_\mathrm{grid} - 1)\cdot\Delta\xi</math></td>
  <td align="center"><math> \theta_i</math></td>
  <td align="center"><math> A</math></td>
  <td align="center"><math> \eta_s</math></td>
  <td align="center"><math> M_\mathrm{tot}</math></td>
  <td align="center"><math> \log10\rho_0</math></td>
  <td align="center"><math> R</math></td>
</tr>
<tr>
  <td align="center">1</td>
  <td align="left">0.05</td>
  <td align="left">0.9995836</td>
  <td align="left">1.00124818</td>
  <td align="left">3.141592582</td>
  <td align="left">2.510</td>
  <td align="left">0.0009044</td>
  <td align="left">1.253</td>
</tr>
<tr>
  <td align="center">2</td>
  <td align="left">0.140555</td>
  <td align="left">0.9967235</td>
  <td align="left">1.0097655</td>
  <td align="left">3.141580334</td>
  <td align="left">2.531</td>
  <td align="left">0.0071264</td>
  <td align="left">1.253</td>
</tr>
<tr>
  <td align="center">18</td>
  <td align="left">1.5894375</td>
  <td align="left">0.7367887</td>
  <td align="left">1.539943947</td>
  <td align="left">2.821678456</td>
  <td align="left">3.467</td>
  <td align="left">0.663285301</td>
  <td align="left">1.126</td>
</tr>
<tr>
  <td align="center">19</td>
  <td align="left">1.6799927</td>
  <td align="left">0.7178117</td>
  <td align="left">1.566601145</td>
  <td align="left">2.775921455</td>
  <td align="left" bgcolor="yellow">3.470</td>
  <td align="left">0.719947375</td>
  <td align="left">1.107</td>
</tr>
<tr>
  <td align="center">20</td>
  <td align="left">1.7705478</td>
  <td align="left">0.6992927</td>
  <td align="left">1.591530391</td>
  <td align="left">2.728957898</td>
  <td align="left">3.465</td>
  <td align="left">0.7767049</td>
  <td align="left">1.089</td>
</tr>
<tr>
  <td align="center">100</td>
  <td align="left">9.0149598</td>
  <td align="left">0.1886798</td>
  <td align="left">1.973119305</td>
  <td align="left">0.841461698</td>
  <td align="left">1.325</td>
  <td align="left">3.62137</td>
  <td align="left">0.336</td>
</tr>
</table>
</td></tr></table>

<table border="1" cellpadding="3" align="center">
<tr>
  <td align="center" colspan="3">
Equilibrium Sequences of <math>(n_c, n_e) = (5, 1)</math> BiPolytropes Having <math>\mu_e/\mu_c = 1.0</math><br />
(viewed from several different astrophysical perspectives)
  </td>
</tr>
<tr>
  <td align="center" colspan="1">(Interface Pressure<math>)^{1 / 3}</math> vs. Radius<br />(Fixed Total Mass)</td>
  <td align="center" colspan="1">Mass vs. Radius<br />(Fixed Interface Pressure)</td>
  <td align="center" colspan="1">Mass vs. Central Density<br />(Fixed Interface Pressure)</td>
</tr>
<tr>  
  <td align="center" colspan="1">
[[File:MuRatio100PressureVsVolumeA.png|350px|center|Pressure vs Volume]]
  </td>
  <td align="center" colspan="1">
[[File:MuRatio100MassVsRadiusA.png|350px|Total Mass vs Radius]]
  </td>
  <td align="center" colspan="1">
[[File:MuRatio100MassVsCentralDensityA.png|350px|Total Mass vs Central Density]]
  </td>
</tr>

<tr>
<td align="center">
<math>\biggl(\frac{\mu_e}{\mu_c}\biggr)^{-4} \biggl(\frac{2}{\pi}\biggr) A^2\eta_s^2</math>
<br />vs.<br />
<math>\biggl(\frac{\mu_e}{\mu_c}\biggr)^3 \biggl(\frac{\pi}{2^3}\biggr)^{1 / 2} \frac{1}{A^2\eta_s}</math>
</td>
<td align="center">
<math>\biggl(\frac{\mu_e}{\mu_c}\biggr)^{-3/2} \biggl(\frac{2}{\pi}\biggr)^{1 / 2} A\eta_s</math>
<br />vs.<br />
<math>\frac{\eta_s}{\sqrt{2\pi}}</math>
</td>
<td align="center">
<math>\biggl(\frac{\mu_e}{\mu_c}\biggr)^{-3/2} \biggl(\frac{2}{\pi}\biggr)^{1 / 2} A\eta_s</math>
<br />vs.<br />
<math>\log_\mathrm{10}\biggl[\biggl(\frac{\mu_e}{\mu_c}\biggr)^{-5/2}\theta_i^{-5}   \biggr]</math>
</td>
</tr>

<tr>
  <td align="left" colspan="3">NOTE: &nbsp; In all three diagrams, the dashed vertical line identifies the value of the abscissa when it is evaluated for the interface location, <math>\xi_i = 1.668462981</math>.  In each case, this vertical line intersects a key turning point along the model sequence.
  </td>
</tr>
</table>

<table border="0" align="center" cellpadding="8"><tr><td align="left">
[[File:DataFileButton02.png|right|60px|file = Dropbox/WorkFolder/Wiki edits/BiPolytrope/TwoFirstOrderODEs/Bipolytrope51New.xlsx --- worksheet = MuRatio100Fund]]Data values drawn from worksheet "MuRatio100Fund" &hellip;

<table border="1" align="center" cellpadding="3">
<tr>
  <th align="center" colspan="7">
Properties of the Marginally Unstable Model
  </th>
</tr>
<tr>
  <td align="center"><math> \xi_i</math></td>
  <td align="center"><math> \theta_i</math></td>
  <td align="center"><math> A</math></td>
  <td align="center"><math> \eta_s</math></td>
  <td align="center"><math> M_\mathrm{tot}</math></td>
  <td align="center"><math> \log10\rho_0</math></td>
  <td align="center"><math> R</math></td>
</tr>
<tr>
  <td align="left">1.6639103</td>
  <td align="left">0.7211498</td>
  <td align="left">1.561995126</td>
  <td align="left">2.784147185</td>
  <td align="left" bgcolor="yellow">3.4698598</td>
  <td align="left">0.709872477</td>
  <td align="left">1.1107140</td>
</tr>
</table>
</td></tr></table>

====Temporary Excel Interpolations====
<font color="red">HERE</font>

<table border="1" align="center" cellpadding="5">

<tr>
  <td align="center" colspan="6"><b>Properties of Turning-Points Along Sequences Having Various &nbsp;<math>\mu_e/\mu_c</math></b></td>
</tr>

<tr>
  <td align="center" rowspan="2"><math>\frac{\mu_e}{\mu_c}</math></td>
  <td align="center" rowspan="2"><math>\xi_i</math></td>
  <td align="center"><math>P_i</math></td>
  <td align="center"><math>R</math></td>
  <td align="center"><math>M_\mathrm{tot}</math></td>
  <td align="center"><math>\log_{10}(\rho_\mathrm{max})</math></td>
</tr>

<tr>
  <td align="center" colspan="2">(Fixed <math>M_\mathrm{tot}</math>)</td>
  <td align="center" colspan="2">(Fixed <math>P_i</math>)</td>
</tr>

<tr>
  <td align="right">1.000</td>
  <td align="right">1.6684629814</td>
  <td align="right">12.03999149</td>
  <td align="right">0.092175036</td>
  <td align="right">3.46986909</td>
  <td align="right">0.712724159</td>
</tr>

<tr>
  <td align="right">0.9</td>
  <td align="right">1.4459132276</td>
  <td align="right">13.67957562</td>
  <td align="right">0.091291571</td>
  <td align="right">3.50879154</td>
  <td align="right">0.688526899</td>
</tr>

<tr>
  <td align="right">0.8</td>
  <td align="right">1.0482530437</td>
  <td align="right">17.09391244</td>
  <td align="right">0.086279818</td>
  <td align="right">3.69798999</td>
  <td align="right">0.58112284</td>
</tr>

<tr>
  <td align="right">0.75</td>
  <td align="right">0.7170001608</td>
  <td align="right">20.48027265</td>
  <td align="right">0.079651055</td>
  <td align="right">3.91920968</td>
  <td align="right">0.484075667</td>
</tr>

<tr>
  <td align="right">0.74</td>
  <td align="right">0.6365283705</td>
  <td align="right">21.40307774</td>
  <td align="right">0.0777495</td>
  <td align="right">3.97973335</td>
  <td align="right">0.464464039</td>
</tr>
</table>