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Re: Ignorance
From: |
Jordi Gutiérrez Hermoso |
Subject: |
Re: Ignorance |
Date: |
Tue, 6 Mar 2012 12:52:03 -0500 |
On 6 March 2012 12:46, Robert T. Short <address@hidden> wrote:
> On 03/05/2012 07:34 PM, John W. Eaton wrote:
>>
>> On 5-Mar-2012, Robert T. Short wrote:
>>
>> | I don't know the dimensions or the direction a-priori. The obvious
>> | answer is 1:N followed by a repmat but there are so many cute little
>> | octave tricks that I was hoping there was something really clever.
>>
>> Given
>>
>> x = 1:4;
>> y = ones (3, 1);
>> z = ones (3, 4);
>>
>> here are the ways I can think of:
>>
>> Repmat:
>>
>> repmat (x, [3,1])
>>
>> Kron:
>>
>> kron (x, y)
>>
>> Indexing:
>>
>> x(y,:)
>>
>> Outer product:
>>
>> y * x
>>
>> Broadcasting:
>>
>> z .* x
>>
>> Are there any others?
>>
>> jwe
>>
>>
> Excellent. The kind of thing I was looking for was the indexing solution.
> Using kron, outer product, sums, broadcasting involve computation so I
> would rather not use them for something like this. Thanks for the tips.
tic-tock them... You may be surprised at which one is fastest.
Also, I'm expecting that this is an intermediate step for a latter
computation, which is why I suggested broadcasting, which does the
latter computation without explicitly doing something as useless as
copying data around.
- Jordi G. H.