Hi Werner,
> On Apr 26, 2017, at 12:34 AM, Werner Benger <[email protected]> wrote:
>
> Probably correct, Quincey might know better how far the hyperslab
> implementation could be modified to allow a negative stride. Maybe it
> wouldn't be much of a change, just there was no need so far to do it. If that
> is the case, then at least it would mean that the "hyperslab grammar" would
> indeed allow operations like transpose (and rotation) of a dataset, just the
> implementation does not support it. That aside, it's probably not efficient
> as it would require multiple hyperslab operations, so a point selection would
> be faster, but for big data and out-of-core data management, sometimes
> seemingly inefficient operations turn out to be better.
>
I like the idea quite a lot. :-) However, it might be quite difficult
to implement. :-( The hyperslabs are “compiled” into [complex] internal data
structures as they are built up, in order to make the I/O operations as fast as
possible. It would be possible to defer that compilation until when the actual
I/O operation occurs, but that would be another layer of data structures, etc.
I believe it would be worthwhile, particularly so that transposes are possible,
but it would definitely be a fair bit of work…
Quincey
>
> On 26.04.2017 00:13, Isaac Gerg wrote:
>> I am not sure if you are allowed a negative stride but even if you are, I
>> believe the transpose still won't work because the stride doesnt stride
>> dimension like numpy but strides across the memory space and wrap is not
>> allowed. Does this line of thinking make sense?
>>
>> On Tue, Apr 25, 2017 at 6:06 PM, Werner Benger <[email protected]
>> <mailto:[email protected]>> wrote:
>> Hi Isaac,
>>
>> it's just thought that it could be done like this:
>> Copy operation: start = 0, stride = 1
>> target_index = 0 + source_index * 1
>> Reflection: start = max_index, stride = -1
>> target_index = max_index + source_index * -1
>> So a negative stride in one dimensions would go "backwards", thus do a
>> reflection in this direction. In practice the stride parameter is probably
>> an unsigned integer and thus running out of bounds instead of
>> going backwards, as you say.
>>
>> Werner
>>
>>
>>
>> On 25.04.2017 23:48, Isaac Gerg wrote:
>>> Hi Werner, thanks for the reply. Let's wrestle with this a bit. So numpy
>>> does their indexing by strides, the stride for each dimension. hdf5 does
>>> their "striding" across the data in the sense of more of a selection than a
>>> stride. I would be inclined to say that even a negative stride wouldnt
>>> allow this. The problem is the stride is a simply stride and not one based
>>> on dimension index so the stride can't wrap so you end up with out of
>>> bounds issues with the datasets. Does this seem right?
>>>
>>> On Tue, Apr 25, 2017 at 5:29 PM, Werner Benger <[email protected]
>>> <mailto:[email protected]>> wrote:
>>> Hi Isaac,
>>>
>>> without proof, but I could imagine it's possible to implement a shear
>>> operation via hyperslabs. If so, then hyperslabs could be used to implement
>>> rotations:
>>> e.g.
>>> https://www.ocf.berkeley.edu/~fricke/projects/israel/paeth/rotation_by_shearing.html
>>>
>>> <https://www.ocf.berkeley.edu/%7Efricke/projects/israel/paeth/rotation_by_shearing.html>
>>> To do a transpose, one would need a reflection in addition to rotation
>>> (e.g. http://techieme.in/matrix-rotation/
>>> <http://techieme.in/matrix-rotation/> ) , and I guess doing this operation
>>> of a reflection is not possible via hyperslabs, so doing a transpose is out
>>> of reach. Probably it would require to allow something like a negative
>>> stride value...
>>>
>>> Werner
>>>
>>>
>>>
>>> On 25.04.2017 22:24, Isaac Gerg wrote:
>>>> Hi Quincy, I just was reading about point selections and was wondering if
>>>> that's the way we would go. Thanks for confirming!
>>>>
>>>> On Tue, Apr 25, 2017 at 4:21 PM, Quincey Koziol <[email protected]
>>>> <mailto:[email protected]>> wrote:
>>>>
>>>> > On Apr 25, 2017, at 1:02 PM, Isaac Gerg <[email protected]
>>>> > <mailto:[email protected]>> wrote:
>>>> >
>>>> > A coworker and I are mulling over if its possible to take a simple 3x3
>>>> > matrix (stored row major) in a dataspace and write it out transposed to
>>>> > disk using a hyperslab. It seems that the grammer provided by start,
>>>> > stride, blocks, and count won't allow for this. We hope we are wrong!
>>>> > It is possible to do this?
>>>>
>>>> Hyperslabs won’t do this, but you could use a point selection
>>>> instead.
>>>>
>>>> Quincey
>>>>
>>>>
>>>>
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>>>>
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>>> --
>>> ___________________________________________________________________________
>>> Dr. Werner Benger Visualization Research
>>> Center for Computation & Technology at Louisiana State University (CCT/LSU)
>>> 2019 Digital Media Center, Baton Rouge, Louisiana 70803
>>> Tel.: +1 225 578 4809 <tel:%28225%29%20578-4809>
>>> Fax.: +1 225 578-5362 <tel:%28225%29%20578-5362>
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>> ___________________________________________________________________________
>> Dr. Werner Benger Visualization Research
>> Center for Computation & Technology at Louisiana State University (CCT/LSU)
>> 2019 Digital Media Center, Baton Rouge, Louisiana 70803
>> Tel.: +1 225 578 4809 <tel:%28225%29%20578-4809>
>> Fax.: +1 225 578-5362 <tel:%28225%29%20578-5362>
>> _______________________________________________ Hdf-forum is for HDF
>> software users discussion. [email protected]
>> <mailto:[email protected]>http://lists.hdfgroup.org/mailman/listinfo/hdf-forum_lists.hdfgroup.org
>> <http://lists.hdfgroup.org/mailman/listinfo/hdf-forum_lists.hdfgroup.org>
>> Twitter: https://twitter.com/hdf5 <https://twitter.com/hdf5>
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>> Twitter: https://twitter.com/hdf5 <https://twitter.com/hdf5>--
> ___________________________________________________________________________
> Dr. Werner Benger Visualization Research
> Center for Computation & Technology at Louisiana State University (CCT/LSU)
> 2019 Digital Media Center, Baton Rouge, Louisiana 70803
> Tel.: +1 225 578 4809 Fax.: +1 225 578-5362
> _______________________________________________
> Hdf-forum is for HDF software users discussion.
> [email protected]
> http://lists.hdfgroup.org/mailman/listinfo/hdf-forum_lists.hdfgroup.org
> Twitter: https://twitter.com/hdf5
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