Except not working in Function

Asked Sep 13 '20 at 14:01

Active Sep 13 '20 at 15:32

Viewed 33 times

I have defined the CirclePlus operator as follows:

Clear[CirclePlus];
SetAttributes[CirclePlus, {Orderless, Flat, OneIdentity}];
CirclePlus[a_ : Except[_CirclePlus]] := a;
CirclePlus[a_?MatrixQ, b_?MatrixQ, c___] := CirclePlus[Plus[a, b], c]
CirclePlus[a_?VectorQ, b_?VectorQ, c___] := CirclePlus[Plus[a, b], c]
CirclePlus[a_?MatrixQ, b_?NumberQ, c___] := 
 CirclePlus[Plus[a, DiagonalMatrix[Table[b, Length[a]]]], c]

Yet, it does not work as expected for the single argument case:

In: CirclePlus[1]
Out: CirclePlus[1]

I expected Out: 1. If I remove the Except[_CirclePlus], I get recursion errors for other operations, but get the desired result in the above case. How can I solve this issue?

Note: Changing it to the in the comments suggested

CirclePlus[a : Except[_CirclePlus]] := a;

Leads to an infinite recursion again:

Message[$IterationLimit::itlim, 4096]

edited Sep 13 '20 at 15:32

asked Sep 13 '20 at 14:01

infinitezero

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It should be CirclePlus[a : Except[_CirclePlus]]. – xzczd Sep 13 '20 at 14:14
If I do it like that, I get the recursion issue again. – infinitezero Sep 13 '20 at 15:29
That should not happen. Have you ClearAll[CirclePlus]; and removed redundant definition(s)? – xzczd Sep 13 '20 at 15:53
1

Does this answer your question? Constructing a function with Flat and OneIdentity attribute with the property that otimes[a]:>a. See especially my answer to the question. – Carl Woll Sep 13 '20 at 15:54

Except not working in Function

0 Answers0