Dear J'ers
I'm using large 3D arrays (voxels), such as
M =: ?400 400 400$100
To add 1 to a bunch of voxels at positions
I =: ?100 3$400
I go like:
timespacex 'M =: (1+(;/I){M) (;/I) } M'
1.3e_5 42048
This was in version 8.07:
JVERSION
Engine: j807/j64/linux
Release: commercial/2018-10-04T15:00:41
Library: 8.07.26
In version 9.01, however: timespacex 'M =: (1+(;/I){M) (;/I) } M'
0.238664 5.36912e8
It became thousands of times slower! I'm doing this hundreds of thousands
of times and it takes weeks instead of minutes.
A multi-dimensional index for amend does not need to be boxed in j901, but:
timespacex 'M =: (1+(;/I){M) I } M'
0.238302 5.36894e8
gives pretty much the same result.
This is with:
JVERSION
Engine: j901/j64avx2/linux
Beta-p: commercial/2019-11-06T09:48:25
Library: 9.01.10
I was wondering whether it happend in { or }, but to my great surprise:
timespacex 'new =: 1+(;/I) { M'
8e_6 21824
timespacex 'M =: new (;/I) } M'
6e_6 20992
So the solution is to do it in two steps !?!?
With unboxed I in step 2, I get even:
timespacex 'M =: new I } M'
2e_6 2560
Am I missing a point? Could I have foreseen this?
Greetings,
Ben
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