MatrixQ
 Usage
• MatrixQ[expr] gives True if expr is a list of lists or a two-dimensional SparseArray object that can represent a matrix, and gives False otherwise.
• MatrixQ[expr, test] gives True only if test yields True when applied to each of the matrix elements in expr.
Notes
• MatrixQ[expr] gives True only if expr is a list, and each of its elements is a list of the same length, containing no elements that are themselves lists, or is a two-dimensional SparseArray object. • MatrixQ[expr, NumberQ] tests whether expr is a numerical matrix. • New in Version 1; modified in 2. • Advanced Documentation.
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