Scalars, Vectors, and Matrices
A vector in the Wolfram Language consists of a list of scalars. A matrix consists of a list of vectors, representing each of its rows. In order to be a valid matrix, all the rows must be the same length, so that the elements of the matrix effectively form a rectangular array.
|VectorQ[expr]||give True if expr has the form of a vector, and False otherwise|
|MatrixQ[expr]||give True if expr has the form of a matrix, and False otherwise|
|Dimensions[expr]||a list of the dimensions of a vector or matrix|