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MathGroup Archive 1998

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strange behaviour



MatrixQ has a strange behaviour:

?MatrixQ
"MatrixQ[expr] gives True if expr is a list of lists 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."

MatrixQ[{{},{}}] gives True because its argument is a list of lists of
equal length. No problem.

Now:
NumberQ[{}] gives False because {} is not a number. I can understand
that.

But:
MatrixQ[{{},{}},NumberQ] gives True, and this seems to me in
contradiction with the definition of MatrixQ[expr, test]

Can somebody explain this to my stupid mind?

-----------------------------------------------

Jean-Marie THOMAS
Conseil et Audit en Ingenierie de Calcul jmthomas@cybercable.tm.fr
+33 (0)3 88 32 93 64
www.cybercable.tm.fr/~jmthomas
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