more math

[lectures/latex.git] / physics_compact / math.tex

diff --git a/physics_compact/math.tex b/physics_compact/math.tex
index ddaebc6..4c8e6f9 100644 (file)
--- a/physics_compact/math.tex
+++ b/physics_compact/math.tex
@@ -11,7 +11,7 @@ A vector $\vec{a}$ of an $N$-dimensional vector space (see \ref{math_app:vector_
 \vec{a}=\sum_i^N \vec{e}_i a_i
 \label{eq:vec_sum}
 \end{equation}
-The scalar product for an $N$-dimensional vector space is defined as
+The scalar product for an $N$-dimensional real vector space is defined as
 \begin{equation}
 (\vec{a},\vec{b})=\sum_i^N a_i b_i \text{ ,}
 \label{eq:vec_sp}
@@ -38,15 +38,16 @@ i.e.\  the basis vectors are mutually perpendicular (orthogonal) and  have unit
 Such a basis set is called orthonormal.
 The component of a vector can be obtained by taking the scalar product with the respective basis vector.
 \begin{equation}
-\vec{e}_j\vec{a}=\vec{e}_j \sum_i \vec{e}_ia_i=\sum_i \vec{e}_j\vec{e}_ia_i=
+(\vec{e}_j,\vec{a})=(\vec{e}_j,\sum_i \vec{e}_ia_i)=
+\sum_i (\vec{e}_j,\vec{e}_i)a_i=
 \sum_i\delta_{ij}a_i=a_j
 \end{equation}
 Inserting the expression for the coefficients into \eqref{eq:vec_sum}, the vector can be written as
 \begin{equation}
 \label{eq:complete}
-\vec{a}=\sum_i \vec{e}_i (\vec{e}_i\vec{a}) \Leftrightarrow \sum_i\vec{e}_i\vec{e}_i=\vec{1}
+\vec{a}=\sum_i \vec{e}_i (\vec{e}_i,\vec{a}) \Leftrightarrow
+\sum_i\vec{e}_i\cdot \vec{e}_i=\vec{1}
 \end{equation}
 if the basis is complete.
-Thus, the very important second part of \eqref{eq:complete} is known as the completeness relation or closure.
+Indeed, the very important identity representation by the outer product ($\cdot$) in the second part of \eqref{eq:complete} is known as the completeness relation or closure.
 
-Todo: outer product ... + explicitly mark scalar product