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MatrixQ

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MatrixQ[m]

gives True if m is a list of equal-length lists.

MatrixQ[m, f]

gives True only if f[x] returns True for when applied to element x of the matrix m.

• • MatrixQ[{{1, 3}, {4.0, 3/2}}, NumberQ]

These are not matrices:

• • MatrixQ[{{1}, {1, 2}}] (* first row should have length two *)

• • MatrixQ[Array[a, {1, 1, 2}]]

Supply a test function parameter to generalize and specialize:

• • MatrixQ[{{1, 2}, {3, 4 + 5}}, Positive]

• • MatrixQ[{{1, 2 I}, {3, 4 + 5}}, Positive]