Matrix
A
matrix is a rectangular table of
elements (usually called
entries), which may be numbers.. We are only going to work with matrices which entries are real numbers.
The horizontal lines in a matrix are called
rows and the vertical lines are called
columns. A matrix with
m rows and
n columns is called an
m-by-
n matrix (written
m ×
n) and
m and
n are called its
dimensions.
(Frecuently an
m-by-
n matrix is said to has an
order of
m ×
n ("order" = "size")).
A 3x3 matrix can be:
While a general mxn matrix is:
that can be written as:
A = (a_{ij} ), where i=1,...,n and j=1,2,...,m
Observe that almost always upper-case letters denote matrices, while the corresponding lower-case letters, with two subscript indices, represent the entries, for example, the (i,j)^{th} entry of a matrix A is most commonly written as a_{i,j}.