Re: Preventing unwanted threading by Inner
- To: mathgroup at smc.vnet.net
- Subject: [mg123498] Re: Preventing unwanted threading by Inner
- From: DrMajorBob <btreat1 at austin.rr.com>
- Date: Fri, 9 Dec 2011 05:55:29 -0500 (EST)
- Delivered-to: l-mathgroup@mail-archive0.wolfram.com
- References: <jbni23$47f$1@smc.vnet.net> <201112081027.FAA19076@smc.vnet.net>
- Reply-to: drmajorbob at yahoo.com
Oleksandr,
I like the simple elegance of your solution, partly because it's easy to
get rid of "coordinate" at any time, as in
coordinate /: Format[coordinate[pts_List]] := pts
{a, b, c}.coordinate /@ {{A, \[Alpha]}, {B, \[Beta]}, {C, \[Chi]}}
% /. coordinate -> Identity
a {A, \[Alpha]} + b {B, \[Beta]} + c {C, \[Chi]}
{a A + b B + c C, a \[Alpha] + b \[Beta] + c \[Chi]}
Bobby
On Thu, 08 Dec 2011 04:27:28 -0600, Oleksandr Rasputinov
<oleksandr_rasputinov at hmamail.com> wrote:
> On Wed, 07 Dec 2011 11:18:27 -0000, Chris Young <cy56 at comcast.net> wrote:
>
>> I'm trying to prevent Inner from expanding my points into coordinates:
>>
>> In[283]:= Inner[Times, {a, b, c}, {{A, \[Alpha]}, {B, \[Beta]}, {C,
>> \[Chi]}}, Plus]
>> Out[283]= {a A + b B + c C, a \[Alpha] + b \[Beta] + c \[Chi]}
>>
>> As I understand it, this has to do with Times being Listable:
>>
>> In[304]:= Attributes[Times]
>> Out[304]= {Flat, Listable, NumericFunction, OneIdentity, Orderless,
>> Protected}
>>
>> But clearing the listable attribute doesn't do anything:
>>
>> Unprotect[Times];
>> ClearAttributes[Times, Listable];
>> myInnnerProd = Inner[Times, {a, b, c}, {{A, \[Alpha]}, {B, \[Beta]}, {C,
>> \[Chi]}}, Plus];
>> SetAttributes[Times, Listable];
>> Protect[Times];
>>
>> In[315]:= myInnnerProd
>>
>> Out[315]= {a A + b B + c C, a \[Alpha] + b \[Beta] + c \[Chi]}
>>
>> In addition, I have to resort to using Hold on the points. Not sure
>> why; I would have thought that making Times non-listable would have
>> been enough.
>>
>> In[343]:=
>> Unprotect[Times];
>> ClearAttributes[Times, Listable];
>> myInnerProd =
>> Inner[Times, {a, b, c}, Hold /@ {{A, \[Alpha]}, {B, \[Beta]}, {C,
>> \[Chi]}}, Plus];
>> myInnnerProd = ReleaseHold[myInnerProd]
>> SetAttributes[Times, Listable];
>> Protect[Times];
>>
>> Out[346]= a {A, \[Alpha]} + b {B, \[Beta]} + c {C, \[Chi]}
>>
>
> Redefining built-in functions in such a drastic way is seldom a good idea
> because Mathematica makes assumptions about the way these functions
> operate and does not handle alterations gracefully. In this case it seems
> that Inner does not check to see if the Attributes set on Times have been
> changed and instead uses a direct internal (kernel) function call as if
> it
> had the default Attributes.
>
> I assume you want this form for display purposes or because you want to
> keep the coordinates as isolated entities. In that case, rather than
> redefining Times, you could use:
>
> coordinate /: Format[coordinate[pts_List]] := pts
>
> {a, b, c} . coordinate /@ {{A, \[Alpha]}, {B, \[Beta]}, {C, \[Chi]}}
>
--
DrMajorBob at yahoo.com
- References:
- Re: Preventing unwanted threading by Inner
- From: "Oleksandr Rasputinov" <oleksandr_rasputinov@hmamail.com>
- Re: Preventing unwanted threading by Inner