Re: column * row ??
- To: mathgroup at smc.vnet.net
- Subject: [mg28847] Re: column * row ??
- From: "Allan Hayes" <hay at haystack.demon.co.uk>
- Date: Tue, 15 May 2001 00:59:21 -0400 (EDT)
- References: <rnIL6.7917$UE4.54583@ralph.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
Some timing info:
v= Table[Random[],{500}];
w=Table[Random[],{1000}];
xx=Outer[Times,v,w];//Timing
{14.45 Second,Null}
yy=(List/@v).{w};//Timing
{1.82 Second,Null}
xx===yy
True
--
Allan
---------------------
Allan Hayes
Mathematica Training and Consulting
Leicester UK
www.haystack.demon.co.uk
hay at haystack.demon.co.uk
Voice: +44 (0)116 271 4198
Fax: +44 (0)870 164 0565
<BobHanlon at aol.com> wrote in message
news:rnIL6.7917$UE4.54583 at ralph.vnet.net...
> n = 5;
> colvec = Table[ToExpression["a"<>ToString[k]], {k, n}];
> rowvec = Table[ToExpression["b"<>ToString[k]], {k, n}];
>
> Outer[Times, colvec, rowvec]
>
> Bob Hanlon
>
> In a message dated 2001/5/12 9:50:46 PM, jrchaff at mcn.net writes:
>
> >Can someone tell me a way to mimic the building of
> >an N x N matrix by multiplying a column vector
> >on left times a row vector on right ? (both vectors
> >of length N) - I mean in Mathematica, of course.
> >
> >i.e, want the result,
> >
> >(colvec){a1,a2, .. aN} * (rowvec){b1,b2,..bN} =
> >
> >result is matrix:
> >
> >{{a1*b1 a1*b2 ..... a1*bN},
> > {a2*b1 a2*b2 ..... a2*bN},
> > ... ... ... ,
> > {aN*b1 aN*b2 ..... aN*bN}}
> >
> >
> >When I try this in Mathematica all I can figure out
> >how to produce is the standard dot-product. If I
> >try the 'transposed' lists/matrices, I get an error,
> >even tho the product is defined by basic rules of
> >matrix multiplication.
> >
>
>