où $$ (r,r_1,r_2) \in \mathbb{R}_+^3. $$
Les hypothèses : $ J $ et $ g $ sont de classe $ \mathcal{C}^2 $.
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-Le Lagrangien de $ \mathcal(P) $ : $ L(x,y,z,\lambda) = $
+Le Lagrangien de $ \mathcal{P} $ : $ L(x,y,z,\lambda) = $
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Le gradient de $ J $ : $ \nabla J(x,y,z) = (\frac{\partial J}{\partial x}(x,y,z),\frac{\partial J}{\partial y}(x,y,z),\frac{\partial J}{\partial z}(x,y,z)) = $
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La matrice hessienne de $ J $ : $ H[J](x,y,z) =
\begin{pmatrix}
- \frac{\partial^2 J}{\partial^2 x} & \frac{\partial^2 J}{\partial x\partial y} & \frac{\partial^2 J}{\partial x\partial z} \\
- \frac{\partial^2 J}{\partial y\partial x} & \frac{\partial^2 J}{\partial^2 y} & \frac{\partial^2 J}{\partial y\partial z} \\
- \frac{\partial^2 J}{\partial z\partial x} & \frac{\partial^2 J}{\partial z\partial y} & \frac{\partial^2 J}{\partial^2 z} \\
+ \frac{\partial^2 J}{\partial^2 x}(x,y,z) & \frac{\partial^2 J}{\partial x\partial y}(x,y,z) & \frac{\partial^2 J}{\partial x\partial z}(x,y,z) \\
+ \frac{\partial^2 J}{\partial y\partial x}(x,y,z) & \frac{\partial^2 J}{\partial^2 y}(x,y,z) & \frac{\partial^2 J}{\partial y\partial z}(x,y,z) \\
+ \frac{\partial^2 J}{\partial z\partial x}(x,y,z) & \frac{\partial^2 J}{\partial z\partial y}(x,y,z) & \frac{\partial^2 J}{\partial^2 z}(x,y,z) \\
\end{pmatrix} =
\begin{pmatrix}
& & \\