diff --git a/config/en/mkdocs.yaml b/config/en/mkdocs.yaml index f3e725a..8d83355 100755 --- a/config/en/mkdocs.yaml +++ b/config/en/mkdocs.yaml @@ -124,6 +124,14 @@ nav: - 'Amplitude modulation': physics/mathematical-physics/signal-analysis/amplitude-modulation.md - 'Signal filters': physics/mathematical-physics/signal-analysis/signal-filters.md - 'Systems': physics/mathematical-physics/signal-analysis/systems.md + - 'Vector analysis': + - 'Vectors': physics/mathematical-physics/vector-analysis/vectors.md + - 'Curves': physics/mathematical-physics/vector-analysis/curves.md + - 'Curvilinear coordinates': physics/mathematical-physics/vector-analysis/curvilinear-coordinates.md + - 'Divergence': physics/mathematical-physics/vector-analysis/divergence.md + - 'Gradient': physics/mathematical-physics/vector-analysis/gradient.md + - 'Curl': physics/mathematical-physics/vector-analysis/curl.md + - 'Vector operators': physics/mathematical-physics/vector-analysis/vector-operators.md - 'Electromagnetism': # - 'Electrostatics': # - 'Magnetostatics': diff --git a/docs/en/physics/mathematical-physics/vector-analysis/curl.md b/docs/en/physics/mathematical-physics/vector-analysis/curl.md new file mode 100644 index 0000000..e69de29 diff --git a/docs/en/physics/mathematical-physics/vector-analysis/curves.md b/docs/en/physics/mathematical-physics/vector-analysis/curves.md new file mode 100644 index 0000000..98eb79d --- /dev/null +++ b/docs/en/physics/mathematical-physics/vector-analysis/curves.md @@ -0,0 +1,88 @@ +# Curves + +> *Definition*: a curve is a continuous vector-valued function of one real-valued parameter. +> +> * A closed curve $\mathbf{c}: \mathbb{R} \to \mathbb{R}^3$ is defined by $\mathbf{c}(a) = \mathbf{c}(b)$ with $a \in \mathbb{R}$ the begin point and $b \in \mathbb{R}$ the end point. +> * A simple curve has no crossings. + +
+ +> *Definition*: let $\mathbf{c}: \mathbb{R} \to \mathbb{R}^3$ be a curve, the derivative of $\mathbf{c}$ is defined as the velocity of the curve $\mathbf{c}'$. The length of the velocity is defined as the speed of the curve $\|\mathbf{c}'\|$. + +
+ +> *Proposition*: let $\mathbf{c}: \mathbb{R} \to \mathbb{R}^3$ be a curve, the velocity of the curve $\mathbf{c}'$ is tangential to the curve. + +??? note "*Proof*:" + + Will be added later. + +
+ +> *Definition*: let $\mathbf{c}: \mathbb{R} \to \mathbb{R}^3$ be a differentiable curve, the infinitesimal arc length $ds: \mathbb{R} \to \mathbb{R}$ of the curve is defined as +> +> $$ +> ds(t) := \|d \mathbf{c}(t)\| = \|\mathbf{c}'(t)\|dt +> $$ +> +> for all $t \in \mathbb{R}$. + +
+ +> *Theorem*: let $\mathbf{c}: \mathbb{R} \to \mathbb{R}^3$ be a differentiable curve, the arc length $s: \mathbb{R} \to \mathbb{R}$ of a section that start at $t_0 \in \mathbb{R}$ is given by +> +> $$ +> s(t) = \int_{t_0}^t \|\mathbf{c}'(u)\|du, +> $$ +> +> for all $t \in \mathbb{R}$. + +??? note "*Proof*:" + + Will be added later. + +## Arc length parameterization + +To obtain a speed of unity everywhere on the curve, or differently put equidistant arc lengths between each time step an arc length parameterization can be performed. It can be performed in 3 steps: + +1. For a given curve determine the arc length function for a given start point. +2. Find the inverse of the arc length function if it exists. +3. Adopt the arc length as variable of the curve. + +Obtaining a speed of unity on the entire defined curve. + +For example consider a curve $\mathbf{c}: \mathbb{R} \to \mathbb{R}^3$ given in Cartesian coordinates by + +$$ + \mathbf{c}(\phi) = \begin{pmatrix} r \cos \phi \\ r \sin \phi \\ \rho r \phi\end{pmatrix}, +$$ + +for all $\phi \in \mathbb{R}$ with $r, \rho \in \mathbb{R}^+$. + +Determining the arc length function $s: \mathbb{R} \to \mathbb{R}$ of the curve + +$$ +\begin{align*} + s(\phi) &= \int_0^\phi \|\mathbf{c}'(u)\|du, \\ + &= \int_0^\phi r \sqrt{1 + \rho^2}du, \\ + &= \phi r \sqrt{1 + \rho^2}, +\end{align*} +$$ + +for all $\phi \in \mathbb{R}$. It may be observed that $s$ is a bijective mapping. + +The inverse of the arc length function $s^{-1}: \mathbb{R} \to \mathbb{R}$ is then given by + +$$ + s^{-1}(\phi) = \frac{\phi}{r\sqrt{a + \rho^2}}, +$$ + +for all $\phi \in \mathbb{R}$. + +The arc length parameterization $\mathbf{c}_s: \mathbb{R} \to \mathbb{R}^3$ of $\mathbf{c}$ is then given by + +$$ + \mathbf{c}_s(\phi) = \mathbf{c}(s^{-1}(\phi)) = \begin{pmatrix} r \cos (\phi / r\sqrt{a + \rho^2}) \\ r \sin (\phi / r\sqrt{a + \rho^2}) \\ \rho \phi / \sqrt{a + \rho^2}\end{pmatrix}, +$$ + +for all $\phi \in \mathbb{R}$. \ No newline at end of file diff --git a/docs/en/physics/mathematical-physics/vector-analysis/curvilinear-coordinates.md b/docs/en/physics/mathematical-physics/vector-analysis/curvilinear-coordinates.md new file mode 100644 index 0000000..e69de29 diff --git a/docs/en/physics/mathematical-physics/vector-analysis/divergence.md b/docs/en/physics/mathematical-physics/vector-analysis/divergence.md new file mode 100644 index 0000000..e69de29 diff --git a/docs/en/physics/mathematical-physics/vector-analysis/gradient.md b/docs/en/physics/mathematical-physics/vector-analysis/gradient.md new file mode 100644 index 0000000..e69de29 diff --git a/docs/en/physics/mathematical-physics/vector-analysis/vector-operators.md b/docs/en/physics/mathematical-physics/vector-analysis/vector-operators.md new file mode 100644 index 0000000..e69de29 diff --git a/docs/en/physics/mathematical-physics/vector-analysis/vectors.md b/docs/en/physics/mathematical-physics/vector-analysis/vectors.md new file mode 100644 index 0000000..a76b5db --- /dev/null +++ b/docs/en/physics/mathematical-physics/vector-analysis/vectors.md @@ -0,0 +1,62 @@ +# Vectors and geometry + +## Axiomatic geometry + +The defining property of axiomatic geometry is that it can be introduced without any reference to a coordinate system. The 5 postulates of classical geometry are listed below. + +1. A straight line segment can be drawn between any pair of two points. +2. A straight line segment can be extended indefinitely into a straight line. +3. A line segment is the radius of a circle with one of the end points as its center. +4. All right angles are congruent. + +The fifth postulate as formulated below is only valid for Euclidean geometry; flat space informally. + +5. Given in a plane, a line and a point not on that line there is only one line through that point that does not intersect with the other line. + +## Vectors + +Referring to linear algebra section [vector spaces](../../../mathematics/linear-algebra/vector-spaces.md) for the axioms of the Euclidean vector space and its vector definitions. Some vector products in 3 dimensional Euclidean space are defined below + +> *Definition*: the Euclidean scalar product of $\mathbf{u}, \mathbf{v} \in \mathbb{R}^3$ is given by +> +> $$ +> \langle \mathbf{u}, \mathbf{v} \rangle := \|\mathbf{u}\| \|\mathbf{v}\| \cos \varphi, +> $$ +> +> with $\|\mathbf{u}\|$ and $\|\mathbf{v}\|$ the length of $\mathbf{u}$ and $\mathbf{v}$ and the $\varphi$ the angle between $\mathbf{u}$ and $\mathbf{v}$. + +It follows than that for $\mathbf{v} = \mathbf{u}$ we have + +$$ + \|\mathbf{u}\| = \langle \mathbf{u}, \mathbf{u} \rangle. +$$ + +> *Definition*: the Euclidean cross product of $\mathbf{u}, \mathbf{v} \in \mathbb{R}^3$ is given by +> +> $$ +> \|\mathbf{u} \times \mathbf{v}\| := \|\mathbf{u}\| \|\mathbf{v}\| \sin \varphi, +> $$ +> +> with $\|\mathbf{u}\|$ and $\|\mathbf{v}\|$ the length of $\mathbf{u}$ and $\mathbf{v}$ and the $\varphi$ the angle between $\mathbf{u}$ and $\mathbf{v}$. Defining the area of a parallelogram span by $\mathbf{u}$ and $\mathbf{v}$. The normal direction of the surface is obtained by not taking the length of the cross product. + +The scalar and cross product can be combined obtaining a parallelepiped spanned by three 3-dimensional vectors. + +> *Definition*: the Euclidean scalar triple of $\mathbf{u}, \mathbf{v}, \mathbf{w} \in \mathbb{R}^3$ is given by +> +> $$ +> \langle \mathbf{u}, \mathbf{v}, \mathbf{w} \rangle := \langle \mathbf{u}, \mathbf{v} \times \mathbf{w} \rangle, +> $$ +> +> defining the volume of a parallelepiped spanned by $\mathbf{u}, \mathbf{v}$ and $\mathbf{w}$. + +Let $J$ be a $3 \times 3$ matrix given by $J = (\mathbf{u}^T, \mathbf{v}^T, \mathbf{w}^T)$, the Euclidean scalar product may also be defined as + +$$ + \langle \mathbf{u}, \mathbf{v}, \mathbf{w} \rangle = \det (J), +$$ + +with $\mathbf{u}, \mathbf{v}, \mathbf{w} \in \mathbb{R}^3$. We also have that + +$$ + \langle \mathbf{u}, \mathbf{v}, \mathbf{w} \rangle^2 = \det (J^TJ). +$$ \ No newline at end of file