Elementwise Multiplication (Dot Multiplication) of Matrices

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Chuck
Chuck 2018-3-24
评论： Star Strider 2018-3-24
I am an instructor of MATLAB at a university. And we traditionally taught that for element-wise multiplication to work, both dimensions (row and column number) of each matrices must be exactly the same. For instance, you could multiply a 1x3 array with another 1x3 array, but not with a 4x1 array. And it used to be like that, otherwise, it would give an error, saying "matrix dimensions must agree".
I just noticed that at least in MATLAB 2017a, you actually can multiply various sizes of arrays element-wise. For example, you can multiply a 1x3 array with a 4x1 array, getting a 3x4 array. However, you still cannot element-wise multiply a 1x3 array with a say, 2x2 array. What is the rule for the dimensions when doing elemnent-wise multiplication there? And in which edition of MATLAB this change occurred?
Thank you.

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Star Strider
Star Strider 2018-3-24
It’s called ‘implicit expansion’, and was introduced in R2016b.
I can’t find a specific link to it. You can find it under Mathematics in the Release Notes (link) for R2016b.
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James Tursa
James Tursa 2018-3-24
编辑：James Tursa 2018-3-24
It applies to any two arrays as long as there is not a mismatch in an index where both dimensions are not equal to 1 and also not equal to each other. So not just for vectors and matrices.

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