Test of whether an object is a matrix:

This is not a matrix because the rows have different lengths:

This is not a matrix because the elements are not lists:

This is not a matrix because the lists are too deeply nested:

Use tests to restrict particular kinds of numbers:

Many different heads can represent a matrix:

A matrix can have rows in different representations of a list:

Format the matrix:

Test for a matrix with numeric entries:

Test for a matrix with explicit numbers:

Test if a matrix has real numeric entries:

Faster test for real-valued numbers:

Test for a matrix of integers:

Test for a matrix of numbers that are integers when rounded to two decimal places:

Test for a matrix of strings:

Test for a matrix of polynomials in x:

Generalize MatrixQ using a test:

The tested expression is not a matrix by the standard definition:

Define a function that only evaluates for explicit matrices:

This represents the Hermitian part of a matrix symbolically:

This gets the Hermitian part explicitly:

A matrix is made up of vectors of equal length:

Confirm with the built-in function:

An empty list is not a matrix:

It is instead a zero-length vector:

A list of empty lists is considered an matrix:

MatrixQ[expr] is equivalent to ArrayQ[expr,2]:

MatrixQ[expr] is equivalent to ArrayQ[expr,2]:

For a depth-4 array arr, MatrixQ[arr,MatrixQ] gives True:

The converse of this statement is False:

MatrixQ effectively uses AllowedHeads"ListLike":