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Single-Particle Electrodynamics - Assassination Science

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A.7.2<br />

Square matrices<br />

Matrices with an equal number of rows and columns are referred to as square<br />

matrices.<br />

The dimensions of a square matrix are thus the same value; this is referred<br />

to as its dimension.<br />

A.7.3<br />

Vectors<br />

A matrix with one only row or only one column is referred to as a vector,<br />

either a row vector, or a column vector, respectively. One of the dimensions<br />

of a matrix that is a vector is thus equal to unity; the other is referred to as<br />

the dimension of the vector.<br />

Three-vectors and four-vectors are special types of vector, which are discussed<br />

in Sections A.8 and A.9. Except for three-vectors, there are no special<br />

symbols to denote vectors.<br />

From the above definitions, it follows that the adjective d-dimensional<br />

may refer to a vector or a square matrix, but no other matrices.<br />

A.7.4<br />

Indices<br />

The position of a matrix element in a matrix is measured by two enumerated<br />

quantities, termed indices.<br />

A matrix symbol is dereferenced by placing the row and column indices<br />

as subscripts on the matrix symbol, with the row index to the left of the<br />

column index; the resulting notation may optionally be placed in parentheses<br />

for emphasis.<br />

The enumeration set used to represent a matrix index’s possible values<br />

must have the same dimension as the corresponding dimension of the matrix,<br />

but it may, in general, have arbitrary offset; in practice, however, the corresponding<br />

enumeration sets are usually either zero-offset or unit-offset, and<br />

344

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