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MathGroup Archive 1995

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Re: list of Mma commands with specified properties

  • To: mathgroup at christensen.cybernetics.net
  • Subject: [mg698] Re: [mg644] list of Mma commands with specified properties
  • From: Richard Mercer <richard at seuss.math.wright.edu>
  • Date: Mon, 10 Apr 1995 13:50:14 -0400

Jack Goldberg writes:

>  Hi Group;
>  	A student asked me "Which Mma commands have the
>  option of allowing Trig->False so that she could
>  set Trig->True?"
>  	This question raises a more general issue which
>  I pose to you in the form of two questions:
>  	(1) How does one ask for a list of commands which
>  	have a
>  	    specified option such as Trig->False ?

Select[ToExpression /@ Names["System`*"],
MemberQ[Options[#],Trig->False]&]

will generate a few errors, then give you pretty much what you're looking for.

>  (I won't clutter cyberspace with my makeshift solution,
>  since I'll bet there is a "professional" way to do it.)
>  	(2) Same question for attributes, say for
>  	instance, Listable?

Pretty much ditto. The following will give even more error messages, 

followed by what you want.

Select[ToExpression /@ Names["System`*"],
MemberQ[Attributes[#],Listable]&]

>  

>  Another student asked this question (actually it was me):
>  	(3) Is there a way of forcing the front end to
>  	produce
>  	     output in MatrixForm in a given Mma session
>  	    rather than a list of lists (of equal length)
>  	    as it does now?
>  This is of value when one knows in advanced that a
>  particular session will be dealing entirely with matrices.

$PrePrint = If[MatrixQ[#],MatrixForm[#],#]]&

makes life worth living again! Every matrix now comes out in MatrixForm  
automatically. Even some you didn't really want to!

Have you ever tried to do further calculations with matrices to which you had  
applied MatrixForm? It doesn't work, because the head MatrixForm stays  
attached! A major pain in the neck, which the $PrePrint solution avoids.

Richard Mercer


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