# How to apply multiple/complicated requirements for a pattern in a function input [duplicate]

In this question. I suggested that to test whether the input of a function was a matrix of numbers one could create the following test:

matrixnumQ[exp_] := MatrixQ[exp, NumericQ]


and then define the function as:

myfunction[W_?matrixnumQ]:=W


This is simple enough in this case but is there a way to test patterns on inputs in a single line if the pattern test is more complex than that above. Something like:

myfunction[W_?MatrixQ[#,NumericQ]&]:=W


This clearly doesn't work but just to give you the idea of what I'm looking for

• You'd better use Condition (/;) taking e.g. Det[W] as a definition, e.g. myfunction[W_ /; MatrixQ[W, NumericQ]] := Det[W]. This question should be interesting: mathematica.stackexchange.com/questions/533/… – Artes May 24 '13 at 1:01
• Thanks @Artes, I wrote an answer below using /; after finding it in another question. Your implementation is better though. If you want to write this as an answer, I'll accept it. – Jonathan Shock May 24 '13 at 1:02
• The last line in your post will work - you just need extra parentheses: myfunction[W_?(MatrixQ[#,NumericQ]&)]. See this question for an explanation. If this was the main difficulty you had here, I'd consider this question a duplicate. – Leonid Shifrin May 24 '13 at 11:20
• Thanks @LeonidShifrin, I would consider that a duplicate and will flag it as such. Thank you. – Jonathan Shock May 25 '13 at 3:51

More straightforward approach would be this:

myfunction[W_ /; MatrixQ[W, NumericQ]]:= definition


e.g.

myfunction[ W_ /; MatrixQ[W, NumericQ]]:= Det[W]


an example:

myfunction[{{1, 3}, {-2, -3}}]

3


if e.g. the input is not a matrix or doesn't satisfy the condition then the function is unevaluated

myfunction[{{a, b}, {c, d}}]

 myfunction[{{a, b}, {c, d}}]


I'd recommend this post Using a PatternTest versus a Condition for pattern matching

OK, I think I figured it out from this question. The answer seems to be:

myfunction[W_?MatrixQ /; Apply[And, NumericQ[#] & /@ Flatten[W]]] := W


Any other suggestions would be great to know.