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  • fujiisoup · 6 ✖

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  • implement Gradient · 6 ✖

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id html_url issue_url node_id user created_at updated_at ▲ author_association body reactions performed_via_github_app issue
423167921 https://github.com/pydata/xarray/pull/2398#issuecomment-423167921 https://api.github.com/repos/pydata/xarray/issues/2398 MDEyOklzc3VlQ29tbWVudDQyMzE2NzkyMQ== fujiisoup 6815844 2018-09-20T12:40:16Z 2018-09-20T12:40:16Z MEMBER

Thanks, @rabernat for the review.

Added the limitation of this method to docs.

 
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   implement Gradient 356698348
422973404 https://github.com/pydata/xarray/pull/2398#issuecomment-422973404 https://api.github.com/repos/pydata/xarray/issues/2398 MDEyOklzc3VlQ29tbWVudDQyMjk3MzQwNA== fujiisoup 6815844 2018-09-19T22:01:12Z 2018-09-19T22:01:12Z MEMBER

Thanks all. Updated.

Thanks, @spencerkclark

Eventually it would be nice if this worked on DataArrays with cftime.datetime coordinates; I think it would be relatively straightforward to modify to_numeric to enable it (we could probably enable it for interp at the same time), but I can take care of that later if you'd like.

Thanks. I added this function for something like this extension, though I do not yet fully follow your cftime update. It would be super nice if you could take care of this after merge.

@shoyer ,

we might want to include an option for periodic boundary conditions

Agreed. This option is nice not only differentiate but also interp and rolling. I think we can add a common logic to take care of them.

@fmaussion

See also #1288 : integrate is the next on my list ;) - I can try to give it a go if @fujiisoup doesn't want to do it himself

Thanks. Actually, I am now moving to another nation and would not have enough time in a few weeks. I will appreciate if you could take care of this.

 
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   implement Gradient 356698348
422639302 https://github.com/pydata/xarray/pull/2398#issuecomment-422639302 https://api.github.com/repos/pydata/xarray/issues/2398 MDEyOklzc3VlQ29tbWVudDQyMjYzOTMwMg== fujiisoup 6815844 2018-09-19T03:35:51Z 2018-09-19T03:35:51Z MEMBER

I think it's ready :)

 
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   implement Gradient 356698348
420474101 https://github.com/pydata/xarray/pull/2398#issuecomment-420474101 https://api.github.com/repos/pydata/xarray/issues/2398 MDEyOklzc3VlQ29tbWVudDQyMDQ3NDEwMQ== fujiisoup 6815844 2018-09-12T00:49:23Z 2018-09-12T00:49:23Z MEMBER

Thanks, @dopplershift .

Aren't you taking differences of values and dividing by differences between the matching coordinates?

Yes, correct. But if we have closer data points, then the estimate of the gradient becomes more precise. Sorting the array according to the coordinate provides the closest points, resulting in the most precise estimate of the gradient.

But I also think users can do it manually before taking the gradient. 

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   implement Gradient 356698348
420458057 https://github.com/pydata/xarray/pull/2398#issuecomment-420458057 https://api.github.com/repos/pydata/xarray/issues/2398 MDEyOklzc3VlQ29tbWVudDQyMDQ1ODA1Nw== fujiisoup 6815844 2018-09-11T23:18:17Z 2018-09-11T23:18:17Z MEMBER

any thoughts for this?

 
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   implement Gradient 356698348
418541019 https://github.com/pydata/xarray/pull/2398#issuecomment-418541019 https://api.github.com/repos/pydata/xarray/issues/2398 MDEyOklzc3VlQ29tbWVudDQxODU0MTAxOQ== fujiisoup 6815844 2018-09-04T22:41:41Z 2018-09-04T22:41:41Z MEMBER

I wonder if we should consider calling this xarray.differentiate instead of xarray.gradient. I think the NumPy function is poorly named for differentiating along a single axis at once.

Agreed. Differentiate is nicer.

Some other api questions arised during the implementation + Do we support differentiate for Dataset? In that case, what should we do for the variables that are independent from the target coordinate? I thought 'keep them as is' is intuitive (and I implemented so), but mathematically, they should be zero.

  • Do we need to sort the array before computing differentiate? np.gradient implicitly assumes the array is sorted (but do nothing about this).
 
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   implement Gradient 356698348

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