1D matrix addition weirdness

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Alex Pedcenko
Alex Pedcenko on 17 Jan 2019
Edited: Stephen23 on 17 Jan 2019
>> ones(5,1)+ones(1,5)
ans =
2 2 2 2 2
2 2 2 2 2
2 2 2 2 2
2 2 2 2 2
2 2 2 2 2
% what?????
% but
>> ones(2,5)+ones(5,2)
Matrix dimensions must agree.
% as expected
% 2014 ver produce error in both cases
Why is this unexpected vecor addition behaviour in recent MATLABs (2017,2018)??????

Accepted Answer

madhan ravi
madhan ravi on 17 Jan 2019
Edited: madhan ravi on 17 Jan 2019
Stephen23 on 17 Jan 2019
Edited: Stephen23 on 17 Jan 2019
"its still weird from mathematics point of view [wrong actually])"
Note that implicit expansion is really just an extension of scalar expansion, which has been part of MATLAB for a very long time: is scalar expansion weird/wrong as well?? A strict language would require all operations to be performed only on exactly compatible array sizes (i.e. the same size for array operations), but not only would this be inconvenient, using repmat all the time would likely be much less efficient than scalar expansion and implicit expansion.
It would certainly be nice if it was possible to select expansion or no expansion.

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