Re: Ignorance

[Jordi Gutiérrez Hermoso]

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.