[Octave-bug-tracker] [bug #48564] Octave does not accept "1 / ND array", "mrdivide (1, ND array)", "mldivide (ND array, 1)"

[Philip Nienhuis]

Update of bug #48564 (project octave):

                 Summary: Octave does not accept 1 / ND array => Octave does
not accept "1 / ND array", "mrdivide (1, ND array)", "mldivide (ND array, 1)"

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Follow-up Comment #3:

Thanks John.

As the Matlab docs are unclear about right division by an array of arbitrary
dimensions, I experimented a bit more.
It turns out that mrdivide, rdivide and "/", and for that matter, mldivide
too, all perform element-by-element division for anything except square
matrices. Obvious as that's the only useful outcome for arbitrary arrays.
Matlab r2016b prerelease:
+verbatim-
>> format long
>> format compact
>> MX = rand (3, 3, 3)
MX(:,:,1) =
   0.327565434075205   0.833500595588975   0.861980478702072
   0.671264370451740   0.768854252429615   0.989872153631504
   0.438644982586956   0.167253545494722   0.514423456505704
MX(:,:,2) =
   0.884281023126955   0.199862822857452   0.825583815786156
   0.588026055308498   0.406954837138907   0.789963029944531
   0.154752348656045   0.748705718215691   0.318524245398992
MX(:,:,3) =
   0.534064127370726   0.136292548938299   0.189710406017580
   0.089950678770581   0.678652304800188   0.495005824990221
   0.111705744193203   0.495177019089661   0.147608221976689

>> (1 / MX) - mrdivide (1, MX)
ans(:,:,1) =
     0     0     0
     0     0     0
     0     0     0
ans(:,:,2) =
     0     0     0
     0     0     0
     0     0     0
ans(:,:,3) =
     0     0     0
     0     0     0
     0     0     0

>> (1 / MX) - rdivide (1, MX)
ans(:,:,1) =
     0     0     0
     0     0     0
     0     0     0
ans(:,:,2) =
     0     0     0
     0     0     0
     0     0     0
ans(:,:,3) =
     0     0     0
     0     0     0
     0     0     0

>> (1 / MX) - mldivide (MX, 1)
ans(:,:,1) =
     0     0     0
     0     0     0
     0     0     0
ans(:,:,2) =
     0     0     0
     0     0     0
     0     0     0
ans(:,:,3) =
     0     0     0
     0     0     0
     0     0     0


For square matrix:

>> SMX = rand (2, 2)
SMX =
   0.054974146906188   0.560559527354885
   0.850712674289007   0.929608866756663
>> 1 / SMX 
Error using  / 
Matrix dimensions must agree. 
>> 1 ./ SMX
ans =
  18.190368678325679   1.783931859509561
   1.175485014180330   1.075721236920778
>> rdivide (1, SMX)
ans =
  18.190368678325679   1.783931859509561
   1.175485014180330   1.075721236920778
>> mrdivide (1, SMX)
Error using  / 
Matrix dimensions must agree. 
>> mldivide (SMX, 1)
Error using  \ 
Matrix dimensions must agree. 



Octave-4.1.0+ does:
+verbatim-
>> 1 / MX
error: operator /: nonconformant arguments (op1 is 1x1, op2 is 3x9)
>> mrdivide (1, MX)
error: mrdivide: operator /: nonconformant arguments (op1 is 1x1, op2 is 3x9)
>> rdivide (1, MX)
ans =
ans(:,:,1) =
   3.05282516399582   1.19975919068585   1.16011908008143
   1.48972602154801   1.30063662500396   1.01023146911583
   2.27974795038665   5.97894649731989   1.94392379926188
ans(:,:,2) =
   1.13086221896275   5.00343178237420   1.21126405445310
   1.70060491533044   2.45727512917771   1.26588202497301
   6.46193746773186   1.33563825635417   3.13947843671169
ans(:,:,3) =
    1.87243431780963    7.33715825105533    5.27119213432779
   11.11720349048724    1.47350858890021    2.02017824743730
    8.95209111422619    2.01947982529240    6.77469037028254
>> mldivide (MX, 1)
error: mldivide: operator \: nonconformant arguments (op1 is 3x9, op2 is
1x1)>>



Is "Matlab compatibility" the proper Item Group or should it rather be one of
"Feature request", "WTF, Matlab?!?" or "Incorrect result"?

And do you want a separate bug report for the ND to 2x2 array conversion?

<title adapted>

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