Re: A possible bug in Lists
- To: mathgroup at smc.vnet.net
- Subject: [mg34429] Re: [mg34392] A possible bug in Lists
- From: BobHanlon at aol.com
- Date: Sun, 19 May 2002 04:14:52 -0400 (EDT)
- Sender: owner-wri-mathgroup at wolfram.com
In a message dated 5/18/02 4:09:47 AM, Klepachd at yahoo.com writes:
>I am having a problem in Mathematica 4.1 :
>
>Evaluating : 1-{1,1} or {1,1}-1 returns {0,0}
>
>Is that ok ?
>
>how is it that I can subtract a vector from a scalar ?
>
Attributes[Plus]
{Flat, Listable, NumericFunction, OneIdentity, Orderless, Protected}
Note that operators such as Plus, Times, Power (as well as many
functions) are Listable. This enables you to act on each element
of a List with a scalar. For example,
mat= {{a11,a12}, {a21,a22}};
mat-b
{{a11 - b, a12 - b}, {a21 - b, a22 - b}}
Plus is also orderless
%==-(b-mat)
True
Times is Listable
mat*b
{{a11*b, a12*b}, {a21*b, a22*b}}
and Orderless
%==b*mat
True
Power is Listable
mat^2
{{a11^2, a12^2}, {a21^2, a22^2}}
But not Orderless
2^mat
{{2^a11, 2^a12}, {2^a21, 2^a22}}
Select[Names["*"], MemberQ[Attributes[#], Listable] &]
Bob Hanlon
Chantilly, VA USA