Commit 18a76890 authored by Claude Meny's avatar Claude Meny

Update cheatsheet.fr.md

parent 269f4e37
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......@@ -91,7 +91,7 @@ visible: false
* Exprimée en coordonnées cartésiennes, l'équation d'onde s'écrit :
<br>
$`\left(\dfrac{\partial^2 f}{\partial x^2}+\dfrac{\partial^2 f}{\partial y^2}+\dfrac{\partial^2 f}{\partial z^2}\right)-\dfrac{1}{\mathscr{v}^2}\dfrac{\partial^2 f}{\partial t^2}=0`$
$`\left(\dfrac{\partial^2 f}{\partial x^2}+\dfrac{\partial^2 f}{\partial y^2}+\dfrac{\partial^2 f}{\partial z^2}\right)-\dfrac{1}{\mathscr{v}^2}\dfrac{\partial^2 f}{\partial t^2}=0`$
<br>
l'expression du laplacien en coordonnées cartésienne étant :
<br>
......@@ -100,12 +100,12 @@ visible: false
* Cherchons les coordonnées cartésiennes du premier terme, $`\overrightarrow{grad}\big(div\;\overrightarrow{E}\big)`$
$`\color{blue}{div\,\overrightarrow{U}=\dfrac{\partial U_x}{\partial x}+\dfrac{\partial U_y}{\partial y}+\dfrac{\partial U_z}{\partial z}}`$
&nbsp;&nbsp;&nbsp;&nbsp;$`\color{blue}{div\,\overrightarrow{U}=\dfrac{\partial U_x}{\partial x}+\dfrac{\partial U_y}{\partial y}+\dfrac{\partial U_z}{\partial z}}`$
* La divergence d'un champ vectoriel est un champ scalaire.
Le gradient d'un champ scalaire $`f`$ est le champ vectoriel, qui s'exprime en coordonnées cartésiennes :
$`\overrightarrow{grad}\,f=\left(
&nbsp;&nbsp;&nbsp;&nbsp;$`\overrightarrow{grad}\,f=\left(
\begin{array}{l}
\dfrac{\partial f}{\partial x}\\
\dfrac{\partial f}{\partial y}\\
......@@ -133,62 +133,62 @@ $`\quad = \left(
\end{array}\right)`$
* Cherchons les coordonnées cartésiennes du deuxième terme, * $`\overrightarrow{rot}\big(\overrightarrow{rot}\,\overrightarrow{E}\big)`$
* Cherchons les coordonnées cartésiennes du deuxième terme, $`\overrightarrow{rot}\big(\overrightarrow{rot}\,\overrightarrow{U}\big)`$
$`\color{blue}{\overrightarrow{rot}\,\overrightarrow{E}=
$`\color{blue}{\overrightarrow{rot}\,\overrightarrow{U}=
\left(\begin{array}{l}
\dfrac{\partial E_z}{\partial y}-\dfrac{\partial E_y}{\partial z}\\
\dfrac{\partial E_x}{\partial z}-\dfrac{\partial E_z}{\partial x}\\
\dfrac{\partial E_y}{\partial x}-\dfrac{\partial E_x}{\partial y}
\dfrac{\partial U_z}{\partial y}-\dfrac{\partial U_y}{\partial z}\\
\dfrac{\partial U_x}{\partial z}-\dfrac{\partial U_z}{\partial x}\\
\dfrac{\partial U_y}{\partial x}-\dfrac{\partial U_x}{\partial y}
\end{array}\right)}`$
$`\overrightarrow{rot}\big(\color{blue}{\overrightarrow{rot}\,\overrightarrow{E}\big)}`$
$`\overrightarrow{rot}\big(\color{blue}{\overrightarrow{rot}\,\overrightarrow{U}\big)}`$
$`\quad =
\left[\begin{array}{l}
\dfrac{\partial}{\partial y}\left(
\color{blue}{\dfrac{\partial E_y}{\partial x}-\dfrac{\partial E_x}{\partial y}}
\color{blue}{\dfrac{\partial U_y}{\partial x}-\dfrac{\partial U_x}{\partial y}}
\right)
-\dfrac{\partial}{\partial z}\left(
\color{blue}{\dfrac{\partial E_x}{\partial z}-\dfrac{\partial E_z}{\partial x}}
\color{blue}{\dfrac{\partial U_x}{\partial z}-\dfrac{\partial U_z}{\partial x}}
\right)\\
\dfrac{\partial}{\partial z}\left(
\color{blue}{\dfrac{\partial E_z}{\partial y}-\dfrac{\partial E_y}{\partial z}}
\color{blue}{\dfrac{\partial U_z}{\partial y}-\dfrac{\partial U_y}{\partial z}}
\right)
-\dfrac{\partial}{\partial x}\left(
\color{blue}{\dfrac{\partial E_y}{\partial x}-\dfrac{\partial E_x}{\partial y}}
\color{blue}{\dfrac{\partial U_y}{\partial x}-\dfrac{\partial U_x}{\partial y}}
\right)\\
\dfrac{\partial}{\partial x}\left(
\color{blue}{\dfrac{\partial E_x}{\partial z}-\dfrac{\partial E_z}{\partial x}}
\color{blue}{\dfrac{\partial U_x}{\partial z}-\dfrac{\partial U_z}{\partial x}}
\right)
-\dfrac{\partial}{\partial y}\left(
\color{blue}{\dfrac{\partial E_z}{\partial y}-\dfrac{\partial E_y}{\partial z}}
\color{blue}{\dfrac{\partial U_z}{\partial y}-\dfrac{\partial U_y}{\partial z}}
\right)\end{array}\right]`$
&nbsp;&nbsp;&nbsp;&nbsp; Nous obtenons alors :
$`\overrightarrow{rot}\big(\overrightarrow{rot}\,\overrightarrow{E}\big)`$
$`\overrightarrow{rot}\big(\overrightarrow{rot}\,\overrightarrow{U}\big)`$
$`\quad =
\left(\begin{array}{l}
\dfrac{\partial^2 E_y}{\partial y\,\partial x}
-\dfrac{\partial^2 E_x}{\partial y^2}
-\dfrac{\partial^2 E_x}{\partial z^2}
+\dfrac{\partial^2 E_z}{\partial z\,\partial x} \\
\dfrac{\partial^2 E_z}{\partial z\,\partial y}
-\dfrac{\partial^2 E_y}{\partial z^2}
-\dfrac{\partial^2 E_y}{\partial x^2}
+\dfrac{\partial^2 E_x}{\partial x\,\partial y} \\
\dfrac{\partial^2 E_y}{\partial x\,\partial z}
-\dfrac{\partial^2 E_x}{\partial x^2}
-\dfrac{\partial^2 E_z}{\partial y^2}
+\dfrac{\partial^2 E_z}{\partial y\,\partial z} \\
\dfrac{\partial^2 U_y}{\partial y\,\partial x}
-\dfrac{\partial^2 U_x}{\partial y^2}
-\dfrac{\partial^2 U_x}{\partial z^2}
+\dfrac{\partial^2 U_z}{\partial z\,\partial x} \\
\dfrac{\partial^2 U_z}{\partial z\,\partial y}
-\dfrac{\partial^2 U_y}{\partial z^2}
-\dfrac{\partial^2 U_y}{\partial x^2}
+\dfrac{\partial^2 U_x}{\partial x\,\partial y} \\
\dfrac{\partial^2 U_y}{\partial x\,\partial z}
-\dfrac{\partial^2 U_x}{\partial x^2}
-\dfrac{\partial^2 U_z}{\partial y^2}
+\dfrac{\partial^2 U_z}{\partial y\,\partial z} \\
\end{array}\right)`$
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; il reste simplement à combiner les résultats :
$`\overrightarrow{grad}\big(div\;\overrightarrow{E}\big)
-\overrightarrow{rot}\big(\overrightarrow{rot}\,\overrightarrow{E}\big)`$
$`\overrightarrow{grad}\big(div\;\overrightarrow{U}\big)
-\overrightarrow{rot}\big(\overrightarrow{rot}\,\overrightarrow{U}\big)`$
$`\quad = \left(
\begin{array}{l}
\dfrac{\partial^2 U_x}{\partial x^2}+\dfrac{\partial^2 U_y}{\partial x\, \partial y}+\dfrac{\partial^2 U_z}{\partial x \,\partial z}\\
......@@ -197,38 +197,38 @@ $`\quad = \left(
\end{array}\right)`$
$`\quad - \quad
\left(\begin{array}{l}
\dfrac{\partial^2 E_y}{\partial y\,\partial x}
-\dfrac{\partial^2 E_x}{\partial y^2}
-\dfrac{\partial^2 E_x}{\partial z^2}
+\dfrac{\partial^2 E_z}{\partial z\,\partial x} \\
\dfrac{\partial^2 E_z}{\partial z\,\partial y}
-\dfrac{\partial^2 E_y}{\partial z^2}
-\dfrac{\partial^2 E_y}{\partial x^2}
+\dfrac{\partial^2 E_x}{\partial x\,\partial y} \\
\dfrac{\partial^2 E_y}{\partial x\,\partial z}
-\dfrac{\partial^2 E_x}{\partial x^2}
-\dfrac{\partial^2 E_z}{\partial y^2}
+\dfrac{\partial^2 E_z}{\partial y\,\partial z} \\
\dfrac{\partial^2 U_y}{\partial y\,\partial x}
-\dfrac{\partial^2 U_x}{\partial y^2}
-\dfrac{\partial^2 U_x}{\partial z^2}
+\dfrac{\partial^2 U_z}{\partial z\,\partial x} \\
\dfrac{\partial^2 U_z}{\partial z\,\partial y}
-\dfrac{\partial^2 U_y}{\partial z^2}
-\dfrac{\partial^2 U_y}{\partial x^2}
+\dfrac{\partial^2 U_x}{\partial x\,\partial y} \\
\dfrac{\partial^2 U_y}{\partial x\,\partial z}
-\dfrac{\partial^2 U_x}{\partial x^2}
-\dfrac{\partial^2 U_z}{\partial y^2}
+\dfrac{\partial^2 U_z}{\partial y\,\partial z} \\
\end{array}\right)`$
$`\quad = \left(\begin{array}{l}
\dfrac{\partial^2 U_x}{\partial x^2}+\dfrac{\partial^2 U_y}{\partial x\, \partial y}+\dfrac{\partial^2 U_z}{\partial x \,\partial z}\\
\quad\quad - \dfrac{\partial^2 E_y}{\partial y\,\partial x}
+\dfrac{\partial^2 E_x}{\partial y^2}
+\dfrac{\partial^2 E_x}{\partial z^2}
-\dfrac{\partial^2 E_z}{\partial z\,\partial x} \\
\quad\quad - \dfrac{\partial^2 U_y}{\partial y\,\partial x}
+\dfrac{\partial^2 U_x}{\partial y^2}
+\dfrac{\partial^2 U_x}{\partial z^2}
-\dfrac{\partial^2 U_z}{\partial z\,\partial x} \\
\\
\dfrac{\partial^2 U_x}{\partial y \,\partial x}+\dfrac{\partial^2 U_y}{\partial y^2}+\dfrac{\partial^2 U_z}{\partial y \,\partial z}\\
\quad\quad - \dfrac{\partial^2 E_z}{\partial z\,\partial y}
+\dfrac{\partial^2 E_y}{\partial z^2}
+\dfrac{\partial^2 E_y}{\partial x^2}
-\dfrac{\partial^2 E_x}{\partial x\,\partial y} \\
\quad\quad - \dfrac{\partial^2 U_z}{\partial z\,\partial y}
+\dfrac{\partial^2 U_y}{\partial z^2}
+\dfrac{\partial^2 U_y}{\partial x^2}
-\dfrac{\partial^2 U_x}{\partial x\,\partial y} \\
\\
\dfrac{\partial^2 U_x}{\partial z \,\partial x}+\dfrac{\partial^2 U_y}{\partial z \,\partial y}+\dfrac{\partial^2 U_z}{\partial z^2}\\
\quad\quad - \dfrac{\partial^2 E_y}{\partial x\,\partial z}
+\dfrac{\partial^2 E_x}{\partial x^2}
+\dfrac{\partial^2 E_z}{\partial y^2}
-\dfrac{\partial^2 E_z}{\partial y\,\partial z} \\
\quad\quad - \dfrac{\partial^2 U_y}{\partial x\,\partial z}
+\dfrac{\partial^2 U_x}{\partial x^2}
+\dfrac{\partial^2 U_z}{\partial y^2}
-\dfrac{\partial^2 U_z}{\partial y\,\partial z} \\
\end{array}\right)`$
* L'ordre de dérivation n'important pas,
......@@ -236,44 +236,46 @@ $`\quad = \left(\begin{array}{l}
nous remarquons alors que toutes les dérivées partielles du second ordre correspondant à
des termes croisés de coordonnées s'annulent :
$`\overrightarrow{grad}\big(div\;\overrightarrow{E}\big)
-\overrightarrow{rot}\big(\overrightarrow{rot}\,\overrightarrow{E}\big)`$
$`\overrightarrow{grad}\big(div\;\overrightarrow{U}\big)
-\overrightarrow{rot}\big(\overrightarrow{rot}\,\overrightarrow{U}\big)`$
$`\require{cancel}\quad = \left(\begin{array}{l}
\dfrac{\partial^2 U_x}{\partial x^2}+\color{blue}{\cancel{\dfrac{\partial^2 U_y}{\partial x\, \partial y}}}+\color{blue}{\cancel{\dfrac{\partial^2 U_z}{\partial x \,\partial z}}}\\
\quad\quad - \color{blue}{\cancel{\dfrac{\partial^2 E_y}{\partial y\,\partial x}}}
+\dfrac{\partial^2 E_x}{\partial y^2}
+\dfrac{\partial^2 E_x}{\partial z^2}
-\color{blue}{\cancel{\dfrac{\partial^2 E_z}{\partial z\,\partial x}}} \\
\quad\quad - \color{blue}{\cancel{\dfrac{\partial^2 U_y}{\partial y\,\partial x}}}
+\dfrac{\partial^2 U_x}{\partial y^2}
+\dfrac{\partial^2 U_x}{\partial z^2}
-\color{blue}{\cancel{\dfrac{\partial^2 U_z}{\partial z\,\partial x}}} \\
\\
\color{blue}{\cancel{\dfrac{\partial^2 U_x}{\partial y \,\partial x}}}+\dfrac{\partial^2 U_y}{\partial y^2}+\color{blue}{\cancel{\dfrac{\partial^2 U_z}{\partial y \,\partial z}}}\\
\quad\quad - \color{blue}{\cancel{\dfrac{\partial^2 E_z}{\partial z\,\partial y}}}
+\dfrac{\partial^2 E_y}{\partial z^2}
+\dfrac{\partial^2 E_y}{\partial x^2}
-\color{blue}{\cancel{\dfrac{\partial^2 E_x}{\partial x\,\partial y}}} \\
\quad\quad - \color{blue}{\cancel{\dfrac{\partial^2 U_z}{\partial z\,\partial y}}}
+\dfrac{\partial^2 U_y}{\partial z^2}
+\dfrac{\partial^2 U_y}{\partial x^2}
-\color{blue}{\cancel{\dfrac{\partial^2 U_x}{\partial x\,\partial y}}} \\
\\
\color{blue}{\cancel{\dfrac{\partial^2 U_x}{\partial z \,\partial x}}}+\color{blue}{\cancel{\dfrac{\partial^2 U_y}{\partial z \,\partial y}}}+\dfrac{\partial^2 U_z}{\partial z^2}\\
\quad\quad - \color{blue}{\cancel{\dfrac{\partial^2 E_y}{\partial x\,\partial z}}}
+\dfrac{\partial^2 E_x}{\partial x^2}
+\dfrac{\partial^2 E_z}{\partial y^2}
-\color{blue}{\cancel{\dfrac{\partial^2 E_z}{\partial y\,\partial z}}} \\
\quad\quad - \color{blue}{\cancel{\dfrac{\partial^2 U_y}{\partial x\,\partial z}}}
+\dfrac{\partial^2 U_x}{\partial x^2}
+\dfrac{\partial^2 U_z}{\partial y^2}
-\color{blue}{\cancel{\dfrac{\partial^2 U_z}{\partial y\,\partial z}}} \\
\end{array}\right)`$
* Au total nous obtenons l'expression simple :
**$`\overrightarrow{grad}\big(div\;\overrightarrow{E}\big)
-\overrightarrow{rot}\big(\overrightarrow{rot}\,\overrightarrow{E}\big)`$**
**$`\overrightarrow{grad}\big(div\;\overrightarrow{U}\big)
-\overrightarrow{rot}\big(\overrightarrow{rot}\,\overrightarrow{U}\big)`$**
**$`\quad =
\left(\begin{array}{l}
\dfrac{\partial^2 U_x}{\partial x^2}\\
\dfrac{\partial^2 U_y}{\partial y^2}\\
\dfrac{\partial^2 U_z}{\partial z^2}\\
\dfrac{\partial^2 U_x}{\partial x^2}+\dfrac{\partial^2 U_x}{\partial y^2}+\dfrac{\partial^2 U_x}{\partial z^2}\\
\dfrac{\partial^2 U_y}{\partial x^2}+\dfrac{\partial^2 U_y}{\partial y^2}+\dfrac{\partial^2 U_y}{\partial z^2}\\
\dfrac{\partial^2 U_z}{\partial x^2}+\dfrac{\partial^2 U_z}{\partial y^2}+\dfrac{\partial^2 U_z}{\partial z^2}
\end{array}\right)`$**
Cette combinaison particulière d'opérateurs $`\overrightarrow{grad}`$, $`\overrightarrow{rot}`$ et $`div`$
constitue la **définition de l'opérateur Laplacien vectoriel** :
**$`\large{\overrightarrow{\Delta}=\overrightarrow{grad}\big(div\;\overrightarrow{E}\big)
-\overrightarrow{rot}\big(\overrightarrow{rot}\,\overrightarrow{E}\big)}`$**
**$`\large{\overrightarrow{\Delta}=\overrightarrow{grad}\big(div\;\overrightarrow{U}\big)
-\overrightarrow{rot}\big(\overrightarrow{rot}\,\overrightarrow{U}\big)}`$**
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