Re: [Blitz-support] any blitz way to combine 1-D and 3-D arrays?

[Patrik J. <co...@fa...>]

A clarification: blitz never creates temporary arrays (even if it
would be advantageous to do so). But in this case it will *evaluate*
the rhs for every value of i,j,k, even if not all of them appear in
the expression.


On Wed, Aug 20, 2014 at 11:36 AM, Patrik Jonsson
<co...@fa...> wrote:
> Yes, the tensor expressions must necessarily evaluate the rhs for
> every element of the lhs. I'm not aware of a way to take yscale and
> copy it into an arbitrary subset of A without a loop. I'm not even
> sure what the syntax for that would look like.
>
>
> On Wed, Aug 20, 2014 at 7:45 AM, Stuart Levy <sa...@il...> wrote:
>> Hmm, thanks, Patrik.
>>
>> That doesn't quite work - BZ_DEBUG reports that it's assigning a rank-2
>> expression to a rank-3 array.
>>
>> It does seem to work if I write all the tensor terms, like
>>
>>      A *=  ( 0*tensor::i + yscale( tensor::j ) + 0*tensor::k );
>>
>> That does seem to create a 3-D expression with the required shape. But
>> is it creating a whole 3D chunk of data to do it?   I suspect it does
>> and wish it wouldn't...  It'd be very wasteful of cache, and I'm trying
>> to do this efficiently on pretty large arrays.
>>
>>
>> On 8/20/14 12:21 PM, Patrik Jonsson wrote:
>>> Hi Stuart,
>>>
>>> I'm a bit rusty, but it seems like
>>>
>>> A = yscale(tensor::j);
>>>
>>> would work?
>>>
>>> Cheers,
>>>
>>> /Patrik
>>>
>>>
>>> On Wed, Aug 20, 2014 at 7:02 AM, Stuart Levy <sa...@il...> wrote:
>>>> Is there any concise Blitz way to do the equivalent of
>>>>
>>>> Array<float,3> A( Nz,Ny,Nx );
>>>> Array<float,1> yscale( Ny );
>>>>
>>>> for i ...
>>>>      for j ...
>>>>        for k ...
>>>>           A(i,j,k) *= yscale(j)
>>>>
>>>> ?
>>>>
>>>> Do I just need to write it as an explicit loop over the 1-D axis?
>>>>
>>>> Or make a goofy (Nz,Ny,Nx) array with a hand-constructed stride vector
>>>> that has the Z- and X-strides equal to zero?
>>>>
>>>> One reason I'd like this: trying to implement curl() over a grid with
>>>> nonuniform spacing on each axis.
>>>>
>>>> If I can write this as an array expression, maybe it can fit in a
>>>> stencil.   Otherwise I'm making a mess of loops which looks a lot like
>>>> the C style I was hoping to avoid...
>>>>
>>>>
>>>> ------------------------------------------------------------------------------
>>>> Slashdot TV.
>>>> Video for Nerds.  Stuff that matters.
>>>> http://tv.slashdot.org/
>>>> _______________________________________________
>>>> Blitz-support mailing list
>>>> Bli...@li...
>>>> https://lists.sourceforge.net/lists/listinfo/blitz-support
>>> ------------------------------------------------------------------------------
>>> Slashdot TV.
>>> Video for Nerds.  Stuff that matters.
>>> http://tv.slashdot.org/
>>> _______________________________________________
>>> Blitz-support mailing list
>>> Bli...@li...
>>> https://lists.sourceforge.net/lists/listinfo/blitz-support
>>>
>>
>>
>> ------------------------------------------------------------------------------
>> Slashdot TV.
>> Video for Nerds.  Stuff that matters.
>> http://tv.slashdot.org/
>> _______________________________________________
>> Blitz-support mailing list
>> Bli...@li...
>> https://lists.sourceforge.net/lists/listinfo/blitz-support