Tables for
Volume B
Reciprocal space
Edited by U. Shumeli

International Tables for Crystallography (2010). Vol. B, ch. 3.1, p. 404   | 1 | 2 |

Section 3.1.2. Scalar product

D. E. Sandsa*

aDepartment of Chemistry, University of Kentucky, Chemistry–Physics Building, Lexington, Kentucky 40506–0055, USA
Correspondence e-mail:

3.1.2. Scalar product

| top | pdf |

The scalar product of vectors u and v is defined as[{\bf u} \cdot {\bf v} = uv \cos \varphi, \eqno(]where u and v are the lengths of the vectors and [\varphi] is the angle between them. In terms of components,[\eqalignno{ &{\bf u} \cdot {\bf v} = (u^{i}{\bf a}_{i}) \cdot (v^{\,j}{\bf a}_{j}) &(\cr &{\bf u} \cdot {\bf v} = u^{i}v^{\,j}{\bf a}_{i} \cdot {\bf a}_{j} &(\cr &{\bf u} \cdot {\bf v} = u^{i}v^{\,j}g_{ij}. &(}%(]In all equations in this chapter, the convention is followed that summation is implied over an index that is repeated once as a subscript and once as a superscript in an expression; thus, the right-hand side of ([link] implies the sum of nine terms[u^{1}v^{1}g_{11} + u^{1}v^{2}g_{12} + \ldots + u^{3}v^{3}g_{33}.]The [g_{ij}] in ([link] are the components of the metric tensor [see Chapter 1.1[link] and Sands (1982a[link])][g_{ij} = {\bf a}_{i} \cdot {\bf a}_{j}. \eqno(]Subscripts are used for quantities that transform the same way as the basis vectors [{\bf a}_{i}]; such quantities are said to transform covariantly. Superscripts denote quantities that transform the same way as coordinates [x^{i}]; these quantities are said to transform contravariantly (Sands, 1982a[link]).

Equation ([link] is in a form convenient for computer evaluation, with indices i and j taking successively all values from 1 to 3. The matrix form of ([link] is useful both for symbolic manipulation and for computation,[{\bf u} \cdot {\bf v} = {\bi u^{T}} {\bi gv}, \eqno(]where the superscript italic T following a matrix symbol indicates a transpose. Written out in full, ([link] is[{\bf u} \cdot {\bf v} = (u^{1} u^{2} u^{3}) \pmatrix{g_{11} &g_{12} &g_{13}\cr g_{21} &g_{22} &g_{23}\cr g_{31} &g_{32} &g_{33}\cr} \pmatrix{v^{1}\cr v^{2}\cr v^{3}\cr}. \eqno(]If u is the column vector with components [u^{1}, u^{2}, u^{3}], [ {\bi u}^{T}] is the corresponding row vector shown in ([link].


Sands, D. E. (1982a). Vectors and Tensors in Crystallography. Reading: Addison Wesley. Reprinted (1995) Dover Publications.

to end of page
to top of page