Commit 1ef55bec authored by Claude Meny's avatar Claude Meny

Update cheatsheet.fr.md

parent d8657608
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......@@ -427,55 +427,7 @@ $`\left.\;+\;\Gamma_{12}^{\;2}\;\overrightarrow{e_2}\cdot\overrightarrow{e_1}\ri
2 \times
\left(\Gamma_{12}^{\;1}\;g_{11}\;+\;\Gamma_{12}^{\;2}\;g_{21}\right)}`$**
Nous obtiendrons l'expression de chaque coefficient individuellement en faisaint en sorte que le coefficient multiplicateur de l'autre soit nul.
Pour cela *multiplions chaque membre de l'équation par $`\mathbf{g^{a1}}`$* :
* **$`\mathbf{\color{blue}{g^{a1}\times}\dfrac{\partial \,g_{11}}{\partial x^2}}`$**
$`\;=\mathbf{\color{blue}{g^{a1}\times}}
\,2\times\left(\Gamma_{12}^{\;1}\;g_{11}\;+\;\Gamma_{12}^{\;2}\;g_{21}\right)`$
<br>
$`\hspace{0,8 cm}=2 \times
\big(\Gamma_{12}^{\;1}\;
\underbrace{\mathbf{\color{blue}{g^{a1}}} g_{11}}_{\large\color{brown}{\mathbf{=\,\delta^{\,a}_{\,1}}}}
\;+\;\Gamma_{12}^{\;2}\;\underbrace{\mathbf{\color{blue}{g^{a1}}} g_{21}}_{\large\color{brown}{\mathbf{=\,?}}}\big)`$
Nous ne pouvons rien dire sur le produit $`g^{a1}g_{21}`$. En revanche en se limitant aux **variétés sans torsion**, nous avons $`g_{ab}=_{ba}`$, l'égalité *$`g^{a1}g_{21}=g^{a1}g_{12}`$ conduit à* :
* $`g^{a1}\times\dfrac{\partial \,g_{11}}{\partial x^2}`$
$`\hspace{0,8 cm}=2 \times
\big(\Gamma_{12}^{\;1}\;
\underbrace{\mathbf{\color{blue}{g^{a1}}} g_{11}}_{\large\color{brown}{\mathbf{=\,\delta^{\,a}_{\,1}}}}
\;+\;\Gamma_{12}^{\;2}\;\underbrace{\mathbf{\color{blue}{g^{a1}}} g_{12}}_{\large\color{brown}
{\mathbf{=\,\delta^{\,a}_{\,2}}}}\big)`$
---
* **$`\mathbf{a=1}`$** induit :
<br>
$`g^{11}\times\dfrac{\partial \,g_{11}}{\partial x^2}`$
$`\hspace{0,8 cm}=2 \times
\big(\Gamma_{12}^{\;1}\;
\underbrace{\mathbf{\color{blue}{g^{11}}} g_{11}}_{\large\color{brown}{\mathbf{=\,\delta^{\,1}_{\,1}\,=\,1}}}
\;+\;\Gamma_{12}^{\;2}\;\underbrace{\mathbf{\color{blue}{g^{11}}} g_{12}}_{\large\color{brown}
{\mathbf{=\,\delta^{\,1}_{\,2}\,=\,0}}}\big)`$
<br>
$`\Longrightarrow\quad`$
**$`\mathbf{\Gamma_{12}^{\;1}=\dfrac{1}{2}\,g^{11}\,\dfrac{\partial \,g_{11}}{\partial x^2}}`$**
---
* **$`\mathbf{a=2}`$** induit :
<br>
$`g^{21}\times\dfrac{\partial \,g_{11}}{\partial x^2}`$
$`\hspace{0,8 cm}=2 \times
\big(\Gamma_{12}^{\;1}\;
\underbrace{\mathbf{\color{blue}{g^{11}}} g_{21}}_{\large\color{brown}{\mathbf{=\,\delta^{\,2}_{\,1}\,=\,0}}}
\;+\;\Gamma_{12}^{\;2}\;\underbrace{\mathbf{\color{blue}{g^{21}}} g_{12}}_{\large\color{brown}
{\mathbf{=\,\delta^{\,2}_{\,2}\,=\,1}}}\big)`$
<br>
$`\Longrightarrow\quad`$
**$`\mathbf{\Gamma_{12}^{\;2}=\dfrac{1}{2}\,g^{21}\,\dfrac{\partial \,g_{12}}{\partial x^2}}`$**
à faire ...
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